When Apple opened its sad little iBooks service in tandem with the iPad, I scoffed: Apple's store offered, then as now, only a small portion of the content available from market leader Amazon Kindle, and those books only worked, then as now, with Apple's lock-in iDevices. Competition? Hardly.

But now that Google has entered the eBook fray, and in a very meaningful way, the tables have turned. Google's new service, called Google eBooks (or Google Books, or Google eBookStore, depending on where you look) offers the first meaningful competition to the Amazon Kindle ecosystem. That said, if this works out the way I think it will, even Kindle users will ultimately benefit from Google's jump into yet another market. But we'll get to that in moment.

In the meantime, what we have is a credible new challenger in the eBook business, offering a library of over three million electronic books, including "hundreds of thousands" for sale. How does this stack up against the Kindle? According to Amazon, it offers 1.8 million free, out of copyright books and over 750,000 "real" books, including 610,000 that are priced at $9.99 or less. The Kindle also offers access to audiobooks (on the Kindle devices), periodicals, and blogs.

Kindle's compatibility store is excellent, with support for Amazon's own devices as well as the PC, Mac, web browsers, Android smart phones, Blackberry smart phones, iPad, iPhone and iPod touch, and Windows Phone 7 (soon). But then, Google's compatibility story is excellent, too, with support for the PC and Mac (via a web browser interface), Android smart phones, iPad, iPhone and iPod touch, and a wide range of dedicated eBook readers, including the Barnes & Noble Nook and Sony Reader lines; basically everything but the Amazon Kindle.

The disparity here is simple: While Amazon is pushing its own proprietary format, Google uses another proprietary format based on the Adobe eBook platform. Before Amazon came around, this format--which works with ePub and PDF files--was broadly supported in the sense that it was used by the handful of poorly-selling devices that then existed. But Amazon obviously shook up the market in a big way.

Google's entry may change all this. In fact, what I'm hoping to see is Amazon open up their Kindle devices and software to the Adobe eBook platform, which would provide eager readers with a best-of-both worlds solution. After all, with your physical book collection, you don't think about where books come from--you could have a book from Borders next to a book from Barnes & Noble on a physical books shelf--and it should be the same way with your electronic book collection. (Likewise, Amazon would be wise to open up its Kindle format to competing eBook readers, though it might run into some resistance there.)

In any event, Google eBooks looks nice, and that includes both the store itself--viewed on the web--and the various software-based readers, including the iPad and web versions I tested.

The store experience works as expected, and unlike a lot of Google UIs isn't underwhelming or overly Spartan. I was particularly interested to see how book prices compared, so I looked up the previous several titles my wife and I purchased on the Kindle to compare prices on Google. Here's how it works out:

Foundation by Asimov, Isaac
Amazon price: $6.29
Google price: $6.07

Decision Points by Bush, George W.
Amazon price: $9.99
Google price: $9.99

Cross Fire by Patterson, James
Amazon price: $14.99
Google price: $14.99

Windows Phone 7 Secrets by Thurrott, Paul
Amazon price: $23.75
Google price: n/a

Full Dark, No Stars by King, Stephen
Amazon price: $14.99
Google price: $12.99

Love Is a Mix Tape: Life, Loss, and What I Listened To by Sheffield, Rob
Amazon price: $8.59
Google price: $9.99

Every Last One: A Novel by Quindlen, Anna
Amazon price: $9.99
Google price: $9.10

Talking to Girls About Duran Duran: One Young Man's Quest for True Love and a Cooler Haircut by Sheffield, Rob
Amazon price: $12.99
Google price: $12.99

Obama's Wars by Woodward, Bob
Amazon price: $14.99
Google price: $12.99

Ape House: A Novel by Gruen, Sara
Amazon price: $9.99
Google price: $9.10

A few trends emerge here. One, f@#$ you, Apple, for allowing publishers to raise the average selling price of new eBooks from $9.99 to $14.99. Readers were better served before you entered the market with iBooks.

Two, Google's prices are actually lower than Amazon's, at least for the ten books we most recently purchased. They are at the very least comparable.

To see what the Google eBooks buying experience is like, I purchased the second book in the "Foundation" series, "Foundation and Empire" by Isaac Asimov. (Confusing, the book "Second Foundation" is the third book in that series, which I vaguely remembered.) The process is simple enough, assuming you're a devoted Google user, since it utilizes Google Checkout, but it's not as simple as Amazon's One-Click goodness.

The browser-based reading experience is pretty darned good, and even better if you have a Tablet PC (few do, I suppose).

The best experience, most likely, is with a dedicated eBook reader. But since I don't have such a thing--my Kindle is giving me forlorn looks as I write this--I fired up my little-used iPad, found and downloaded the Google Books app, and gave that a shot as well. In addition to a handful of free books--Alice's Adventures in Wonderland, Pride and Prejudice, and Great Expectations, my purchased book showed up automatically and looked great. (And while the book itself isn't in color, the cover is, and looks great on the iPad's large screen.)

Best of all, Google Books navigated me automatically to the point to which I had read (via the web interface). So I moved ahead a few pages, noted where I was, and then fired up the web client again. Voila! Just like the Kindle, it remembered where I was, and navigated to the right page. Good stuff.

The iPad version of the Google Books app features the same annoying and unnecessary page-turning effect as Apple's puketastic iBooks app, and I don't see a way to turn that off yet. (Again, I blame Apple for this silliness. Mimicking real world objects is bad UI, especially when it's gratuitous.) But the app does feature a cool magnification feature: Just tap and hold anywhere on the page.

It's still early days, and anything could happen, but I'm pretty sure Google's entry into this market is going to shake things up, and pretty dramatically. Even Apple has had its effect--in addition to the aforementioned price hike on books, Apple has inspired Amazon to reduce the prices on its Kindle devices, which is just wonderful--but I think Google will cause more profound changes here. If Amazon is interested in retaining its lead, it should open up the Kindle ecosystem on both ends, supporting protected ePub/PDF files on its devices and pushing its Kindle books to competing devices like the Nook and Sony eReader. Such moves would benefit consumers in huge and immediately obvious ways, and that's what really matters.

Barring that, Google has at least created a credible challenger to the Kindle, the first such challenger that's really had a chance. If Amazon doesn't open up the Kindle, it will no doubt cede huge market share numbers to this new entry. It's that good.