I have an Xbox, and I really like it. Halo is, hands down, the best FPS I've ever played. I never liked Doom or Quake or any of that type of game, but Halo had me hooked from the beginning. Halo 2 looks to be even more impressive, but probably won't be out til late next year. Brute Force, while not as good as Halo, is also excellent. Star Wars: Knight of the Old Republic, an RPG by Bioware (makers of Baldur's Gate and Neverwinter Nights) will be out in a couple of weeks and looks to be excellent. The upcoming Ninja Gaiden game looks like it's going to be great, too.
The weakest point of the Xbox as it stands now is the lack of RPGs. Right now, there's only Morrowind and Shenmue 2. The next six months should be bringing some strong offerings in that area, though. Pirates of the Carribean comes out this week, I think, the above-mentioned Knights of the Old Republic is out in a couple of weeks, Gladius is scheduled for August, and Sudeki is supposed to be out this fall. Also, if Xbox owners are lucky, Fable, which looks like it's going to be completely friggin' astounding, will be out sometime early next year.
Also note that while some of my favorite Xbox games (Splinter Cell, Hitman 2, NBA Street vol. 2) are out for Playstation, too, they typically have better graphics on the Xbox, and I personally think that the small Xbox controller is the best console controller out there.
If you like online gaming, Xbox is also the most advanced in that area at this point, owing to the Xbox Live network. This isn't something I'm really into, but if you are, it's worth considering.
Finally, Xbox definitely looks like it's the one of the "Big Three" with the brightest future in terms of upcoming games. PS2 is probably close to peaking in terms of what can be got from the system, and the GC has some titles coming up that look promising, but nothing that looks absolutely astounding. The Xbox, on the other hand, has a number of titles scheduled to come out within the next year or so that look like they're going to be mind-blowing.
On the other hand, I also have a GameCube. Now, if I had to pick just one of the two to stick with, I'd definitely go with the Xbox, as it just has a bigger library of better games. On the other hand, the Cube has a few exclusive games that are really, really great. In my opinion, if you can afford it, Metroid Prime and Zelda alone are worth the cost of the system. Throw in other fun games like Eternal Darkness, Super Monkeyball 2, Super Mario Sunshine, etc., and you'll definitely get your money's worth out of the Cube. I think of the Cube as an ideal second system - it doesn't have a big enough library to really be a completely fulfilling primary system, but if you're looking for a smaller number of games that aren't available anywhere else, then the Cube has some really interesting stuff. Since you already own a PS2, this might be what you're looking for.
In the end, you can't really go wrong either way. Both systems have enough really fun games out already that you'll be sure to get your money's worth out of either of them.
drquestion (who loves both his Xbox and his GameCube)
P.S. Sorry about the length of this reply. I got a little carried away.
