Nice little game. It's one of the more simplistic tower defense games I have played, and I'm pretty sure it's just ported from iOS. But if you are new to the genre and want to learn, or want some light fun on your netbook, it's well worth the cheap price tag.
A couple small gripes: there is no in-game music. The only music is on the title screen. Also, it has almost no graphics options and runs only at a 4:3 aspect ratio. The frame rate is capped at 30fps but it doesn't really matter for a slow 2D game like this. Overall, though, if you are looking for a cheap little tower defense game to keep you busy this should fit the bill.