Well, my reason list here is going to be freaking huge compared to my PS2 list, because with the PS2, I would actually buy one if I wasn't a Nintendo person. I would NEVER buy an Xbox.
1) It's made by MS, and partners are nVidia and Intel. It just doesn't start out in a much more evil way.
2) The controller is the worst thing I have felt since the Atari 2600 controller.
3) The "system seller" game known as "Halo" just bites.
4) DOA Xtreme Volleyball is considered a system seller in some circles.
5) It's greatest games are just crappy PC Ports, and I hate PC Games.
6) It would take 2 hours of searching to find a single game for the system I MIGHT actually buy. I was once really upset that I wouldn't get to see Ninja Gaiden on GameCube, but I realized that I didn't even want the game when I found out that it's a Ninja Gaiden game in nothing but name. If I want to play a crappy sequel, I can just go play Chrono Cross.
7) People who like the system say that it's great because you can install Linux on it and run all sorts of emulators. They seem to forget to mention that they can do all of this because of an ILLEGAL SDK release, and the games you are running are also illegal, and any '90s era PC can do the same bloody thing.

The architecture just pisses me off. Any case modder can make an Xbox. Just take a bunch of mid range PC parts, throw them in a box and call it a console. Yay. What pisses me off even more about this is that people actually think that because the Xbox has all this PC stuff, it's more powerful than a GCN. Last I heard, PC architecture was incredibly inefficient as far as gaming is concerned, and I don't see the Xbox improving on the design any.
Xbox can just suck the big one.