Despite its Outlook Express underpinnings, Windows Live Mail has always been a decent email client, offering support for multiple email accounts (including native Hotmail-type account support), centralized contact list management, USENET newsgroup and RSS feed support, and, starting in the wave 3 version, a calendar component that works with Windows Live Calendar as well as, in limited form, third party online calendars. It works offline, which can be handy since Microsoft's web solutions don't support this functionality.
In wave 4, Windows Live Mail is updated in significant ways. First, it takes on a new ribbon-based UI, which is both attractive and functional, and when combined with the new "Quick Cal" calendar pane, much more Outlook-like. Of course, like Outlook, Mail benefits from copious amounts of onscreen real estate: If you're running this application at 1366 x 720 or lower, you're going to have to make some adjustments.
And while Mail doesn't drag your PC down from a performance perspective, as Outlook can, it does support other Outlook niceties. For many email accounts, you can simply enter your email address and password, and Mail will figure out the correct settings. (But it still doesn't work with Exchange accounts.) It's even Gmail-friendly, with an understanding of the Gmail folder structure (which aren't really folders, but whatever), so it surfaces Gmail-specific folders like Sent Items, Drafts, Junk E-mail, and Trash into the standard folders list, and doesn't force you to dive into the weird [Gmail] folder structure like other clients.
It also supports Outlook-like features such as Conversation View, oddly enabled here, though it's disabled by default in Outlook 2010.
Naturally, Mail now integrates nicely with new Hotmail wave 4 features. For example, if you want to share photos with others, you can create a new Photo E-Mail. When you attach a collection of pictures, Mail will assume you want to use the new Hotmail functionality where photos are stored, temporarily, on SkyDrive, instead of clogging up the pipes at your recipient's Internet connection. This provides a number of advantages, not the least of which is the ability to share far more photos than would otherwise be possible. And the presentation is really nice, with customizable templates. Photos sent through SkyDrive can be configured to expire (and thus be deleted) after 90 days, or they can stay in the cloud until you remove them manually. (And if you want to, you can of course go old-school and just attach the photos normally.)
Thanks to that new ribbon UI, some features that were previously buried or unavailable are now more easily summoned. On the View tab, for example, you can now quickly toggle the display of UI pieces you don't want cluttering the display, like Quick views, Storage folders, the status bar, and so on.
There's also some nice Office integration, so that if you paste in content from Office documents, such as those created by Word, the content will retain its original formatting.
I was particularly interested in the Calendar component, since this piece seemed a bit unfinished in wave 3. There's still no tasks/to-do functionality, and no work week view, which I find odd. And you can't add Internet calendars from this UI--presumably you need to do this from the web version of Windows Live Calendar instead. Calendars you add from the web interface do indeed show up in the native app automatically.
Overall, Windows Live Mail remains a useful application, especially for those with Hotmail-type email accounts. I prefer it to Outlook for this purpose, and by a wide margin. Mail is also useful for those who maintain multiple email accounts and don't wish to aggregate them under a single account (which I do). Using the Mail Quick views feature, you can easily view all unread email from all accounts, without having to manually configure one of your email accounts to poll your other accounts. I suspect this will be interesting to many people.
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