First things first I don't hate the Wii, but I definitely don't like it much. And I have one (my parents do anyways) so I've played it more than enough to form an opinion.
1. I have been Playstation all the way since I started playing video games in the late 90's...so that means I have no nostalgic attachment to Nintendo or any of its series like Mario, Zelda, etc. So that means I can actually be objective and not just rate every game with Mario or Zelda in the title as a 10/10.
2. It has brutal online
3. It lacks good games, and by that I really just mean 3rd party games.
4. I'm not big on motion controls. They're sorta fun for like tennis/golf games when you have a bunch of friends over, but when I play video games I just want to sit on my couch and not move for a couple hours...I don't want a workout. I don't need to work out since I'm a gun owner.
5. I will admit I do kinda hate it for its success. I mean its hardly that much more powerful than the Gamecube, it just sold well because of motion controls and low price point. I feel like Nintendo just got lucky so I am a bit sour about that. But this point is more the 2007-08 version of me talking...the 2011 version of me isn't a fanboy anymore.