That came out quite a while ago, November 2005 to be exact.
If you're wanting a game player for emulators, it'd be a fairly good purchase. If you're looking for a PDA that's really good with games, or really PDA at all, it wouldn't be to your liking. If you're looking for an interesting embedded platform, its dual-core ARM9 CPU (one with MMU, one without) should prove interesting.
Plenty of hacking (both hardware and software) going on with it, since it was designed with homebrew in mind. I've been considering one for a while (since before it was released), but its lack of touch screen, lack of RAM (only has 64MB), and lack of 3D processor has put me off.
General overview and specs:http://en.wikipedia.org/wiki/Gp2x
Adding a GPS module internally:http://www.spritesmods.com/?art=gp2xgps
Adding Internal USB host port:http://www.spritesmods.com/?art=gp2xusb