Frankly, there's really no need to tell you how the game works (I think we've all played it at least once), but I will tell you a few things before downloading. First, as with all three PopCap exclusives, Plants vs. Zombies is a Wi-Fi-only download. Second, the file size is approximately 75MB.
Lastly, despite the small number of Android phones in the compatibility list on Amazon's site, we can verify that it also works on the HTC Thunderbolt, HTC Droid Incredible, and the HTC EVO (which are not listed).
Suffice it to say that it will work on the majority of Android phones to date. The app is supposedly not optimized for tablets--pixelation may occur--but if you have one, screw it; try anyway.
On Amazon's Appstore for Android you can download the full, ad-free version of the Plants vs. Zombies. It's free on launch day, then will go back to the standard retail price after the one-day promotion expire, at $2.99. Plants vs Zombies will remain an Amazon exclusive for only two weeks, then becomes available everywhere else.
Plants vs. Zombies will be Amazon's free App of the Day until 3 a.m. ET/12 a.m. PT tonight.