The Nokia Lumia 900 is a great smart phone, with a killer price, an amazing and trend-setting form factor, and unique Nokia apps and services that put it over the top when compared to other Windows Phone handsets. But the key differentiator between device and the iPhone and Android is that it runs on the Windows Phone OS. And let’s not forget what this mobile platform brings to the party ... both good and bad.

When I plotted out what I wanted to write about the Nokia Lumia 900, spreading it out over some number of days that was then to be determined, I had placed an article about the underlying OS, Windows Phone 7.5, much higher up—or sooner, if you will—than was eventually the case. My original thinking was that while Windows Phone 7.5 is obviously central to the Lumia 900, it’s still mostly an unknown for most potential customers.

Eventually, the Windows Phone 7.5 discussion got pushed further back into this series of articles because I felt that it was more important to focus first on those aspects of the Lumia 900 that were unique to that device. So in earlier articles, I’ve examined such things as the Lumia 900 hardware build quality, the device’s LTE and tethering capabilities, the camera, and the Nokia apps and services. If you’ve been reading along, you know that it’s mostly good news but with some areas that need improvement.

So it is with the Windows Phone OS. And while I do—and will here—make the case that the net score for Windows Phone is overwhelmingly positive, it’s important to know what you’re getting into. And that includes the bad with the good.

The biggest problem Windows Phone has, frankly, is perception. Thanks to clueless, ivory tower tech pundits and bloggers who can’t see past their own biases, many believe that Windows Phone and/or Nokia is doomed, and that a supposed lack of apps, or key apps, or certain apps, will carry this thing down just as surely as did the iceberg to the Titanic 100 years ago. But as with the causes of that actual disaster, things here aren’t so simple. And the supposed lack of apps is simply not a problem at all. In fact, this is simply the new version of the “lack of cut and paste” argument from late 2010, a bogus criticism that one can easily toss out to try and discredit the product. But when you argue that things like this are a problem, you’re really just betraying a lack of sophistication. Cut and paste wasn’t a problem in late 2010. And apps are not a problem today.

(Again, I’ve already written about this topic in Don’t Fear the Windows Phone App Apocalypse. Check it out if you haven’t already.)

But there are some real problems with Windows Phone, issues that do in fact affect one’s daily use of the device in negative ways. These are the things that Microsoft and Nokia need to fix, sooner rather than later.  And these issues include:

iCloud. Windows Phone needs an iCloud, or wpCloud, a service that sits up in the Internet somewhere and automatically backs up everything on the phone. And I mean everything: Ringtones, apps, app and phone settings, accounts, pictures, music and other content, voice mails, text messages, and so on. You should be able to buy a new phone, restore from a wpCloud backup and be back and running with everything intact. Everything. This is a huge and missing feature today, and it will still be a huge and missing feature with Windows Phone 8. And that sucks.

(That Windows Phone’s predecessor, Windows Mobile, basically had this exact service—called My Phone—makes this situation even more painful. Just saying.)

Auto photo uploading. Right now, Windows Phone is the only major smart phone which cannot automatically and silently backup every single picture on the phone to a cloud service in full resolution and quality. Instead, we get a lackluster backup feature that is designed only for sharing, so we get low-quality, lower resolution photos saved to SkyDrive. This feature is perhaps worse than useless, and I’m hoping and expecting it to change with Windows Phone 8. (And yes, it could be part of wpCloud. Given that we’re not getting wpCloud anytime soon, this should happen first.)

Service integration. Windows Phone’s deep integration bits are its greatest strength, but also its greatest weakness. And the issue is multi-fold. For example, Windows Phone has nice Facebook integration so that you can do things like check-in, post updates, post photos, and so on, without installing or configuring an app. It’s just built-in. So you snap a photo, choose Share, and you’re off and running. But the problem with this kind of integration is that it can’t keep up with changes in the underlying services, and is dependent instead on the schedule for OS updates. So while, yes, you can check in on Facebook with Windows Phone 7.5, what you can’t do is check others in or add a photo with caption to that check-in. To do that, you need the Facebook app, which is updated more frequently. This kind of “last mile” completeness is an issue with virtually every integrated service, and while it doesn’t render this integration worthless, it sort of does render this integration worthless, if those are the features you want.

Hub extensibility. Windows Phone is wonderfully extensible in some ways, but not in some ways that I think would matter to many people. So, you can integrate SkyDrive and Facebook photo albums into the Pictures hub very nicely, but you can’t add, say, Flickr or Google Picasaweb/+ photo albums, or those of other services, because those hubs aren’t extensible by third parties. Maybe Microsoft will add support for Flickr or your favorite service in Windows Phone 8. Maybe they won’t. What they should really do, however, is make it possible for others to add that support. And I just don’t see it happening.

PC-free usage. If I could change only one thing about Windows Phone today, it would be the photo uploading bit. But if I could change two, I’d add this: For certain tasks today—photo downloading, music, video, and podcast sync, software updates, and the like—you simply have to plug your Windows Phone into a PC via a USB cable and use the horrible and now abandoned Zune PC software. This is simply untenable, but my understanding is that Windows Phone will finally go truly PC-free with Windows Phone 8 later this year. I cannot wait.

So that’s the bad news.

Those are the issues that Windows Phone fans are stridently hoping no one will bring up, until of course they’re fixed, when we can all wax on about how wonderful Microsoft is for making us happy. It’s a list, not insurmountable, but a list nonetheless. I wish this stuff was better.

Now the good news. And it goes like this. Virtually everything else about Windows Phone isn’t just excellent, it’s better—much better—than the experience on competing smart phones like Android and the iPhone. And in my opinion, the good news outweighs the bad by a long shot. There’s so much of it, in fact, that I’ll never get to all of it.

But here’s what hits me right off the top of my head...

Glance and go. Windows Phone hits an amazing middle ground between Apple’s static and bland iOS icons and Google’s requirement to use a subset of widgets to get more detailed information from apps without resorting to opening each app. The core of this is the Start screen live tiles, which can each offer up tons of information, not just a count of unread emails or whatever. In the core app set that comes with Windows Phone, this means a Calendar tile that shows the next appointment. Pictures and Music + Videos tiles that display rich photo and band imagery, respectively.  A People tile that animates little images of your contacts, a feat that still brings a smile to my face every day. A Me tile that keeps you up to date on new interactions. And so on.

These built-in capabilities are extended fairly dramatically by third party apps which can display their own unique rich information, such as weather forecasts, map data, and more. And with new advanced capabilities in Windows Phone 7.5, apps can present even more data, including so-called “deep links” that create tiles for a certain part of an app instead of the app itself; for example, with OneNote Mobile, you can pin a tile that represents an actual note instead of just one for the app itself. Brilliant.

Pocket to Picture. The makers of Android and iOS are starting to figure out that this Windows Phone advantage is truly an advantage and they’re racing to copy it. But the iPhone lacks a dedicated camera button, making its copy-cat feature in the latest iOS revision inherently less efficient. You’ll never miss a shot again with Windows Phone, though, nor will you have to remember where that Camera app is on your numerous home screens.

Designed by designers, not by a committee of one. Apple gets a lot of credit for its design, but let’s face it: The iOS software is a mind-numbingly useless grid of static icons, not something useful or beautiful. Windows Phone was designed by actual designers, not a dictatorial micro-manager, and it shows, via the live tiles, copious uses of white space, beautiful typographic design, and an inherent belief that the designs of each experience in Windows Phone should be “authentically digital.” That is, you don’t make a calendar app look like a desktop calendar that no iPhone user has ever actually used, you make one that’s efficient and beautiful and, yes, digital, with capabilities that are better than the real world object the app doesn’t have to emulate. That type of design—a calendar app that looks like a paper calendar, or a notebook that looks like a pad of paper—isn’t just bad design, or lazy design, it’s inefficient. Digital objects can and should be more efficient and usable than real world objects. Why hobble them?

Integrated experiences, not apps. With all the hand-wringing over Windows Phone’s faux lack of apps, the one thing that non-Windows Phone users don’t seem to get is that apps can be largely unnecessary on this platform, at least in day to day use. You can check your schedule, monitor whether you have any pending voice mails, messages, emails, or Xbox LIVE game requests, see the weather forecast, and more, all without actually leaving the Start screen. On other mobile platforms, it’s whack-a-mole, in and out of individual and isolated app experiences all day long. On Windows Phone, you can share via Twitter, Facebook, LinkedIn, or Windows Live ... without installing an app.  You just do it naturally from wherever you are.

Oh, and apps too. OK, people love apps. Which is fine. We have over 80,000 of them. Enjoy.

Integration with the services people really use. After four+ years of iOS, Apple is finally starting to figure out that people want integrated experiences. So in the latest version of that OS, Apple finally added one support for exactly one integrated service, Twitter. (But even then, you have to manually log in on each device.) Windows Phone integrates with the services people actually use: Facebook, of course, but also Twitter and LinkedIn. And for you Microsoft folks, there’s integration with Windows Live, Xbox LIVE, and Zune.

Best. Email. App. Ever. Other mobile apps range from acceptable to very good, but with Windows Phone 7.5, Microsoft has the best mobile email app I’ve ever used. It’s not just beautiful to look at with the nicest typography treatment ever seen, it’s also infinitely malleable. By this I mean that you don’t just get one instance of the Mail app, you get one for each account. Or you can mix and match some email accounts in one or more linked inboxes, while keeping others separate. Android forces two email apps down your throat—one for Gmail and one for everything else—and each works very differently. On iOS, all your email is funneled through one email app only. Windows Phone gives you more choices. And the best presentation.

Simple multitasking that really works. Remember when the lack of cut and paste and multitasking were supposed big issues for Windows Phone? Probably not, since we have both now. And as a relative newcomer to the space, Windows Phone offers the simplest and most efficient smart phone multitasking I’ve seen, with a simple, card-based UI and intelligent app sleeping and then killing behavior that happens automatically in the background.

Microsoft Office with SkyDrive and SharePoint integration. Windows Phone 7.5 is the only smart phone OS to offer a first-class Microsoft Office experience, with Mobile versions of Word, Excel, PowerPoint, and OneNote, but also deep integration with the document stores on both SkyDrive (for consumers) and SharePoint (including Office 365, for businesses). And this connection is automatic: When you sign-in with your account for email, the corresponding document store is turned on in Office Mobile. Bingo.

Xbox LIVE games. Both iOS and Android offer great games libraries, but only Windows Phone offers actual Xbox LIVE integration with Xbox LIVE games (complete with achievements, multiplayer capabilities, and more), and of course the ability to manage your Xbox LIVE gamertag and interact with your contacts online.

Zune Pass. Microsoft’s $9.99 per month Zune Pass is still my favorite streaming music service and Windows Phone is the only smart phone that offers it. But you can of course choose from other services, like Spotify, if you’d prefer.

There’s a lot more, but of course, I recommend simply going back and checking out my original Windows Phone 7 and Windows Phone 7.5 reviews and other articles for a complete rundown on what make Windows Phone special. What’s amazing is that I created the above list without referring to anything. That’s just what I think of immediately when I think about why I prefer Windows Phone.

I love Windows Phone. And the thing is, I think that most people who come to Windows Phone love it too. The big difference between them and iPhone or Android users, so far at least, is that unlike those people, Windows Phone users tend to have used other smart phone platforms first. And their love of Windows Phone is perhaps more meaningful because they actually have experiences with at least one other system too. I bet most iPhone users simply stop looking around and have no idea what they’re missing. And they’re missing a lot.