I've always been against first person shooters for two reasons:
1) It's a game devoted to violence. There is no other purpose to play a FPS other than to wreak havoc.
2) The few times I tried playing the original Castle Wolfenstein at my cousins' house, I sucked. Not surprising, since I hadn't had any practice.
The guys here at work all like to play FPSs, and they started playing them at lunch or after hours on the LAN. They asked if I wanted to play, but I wasn't really interested. But I felt left out. Now, I could have loaded up a strategy game or a RPG, but what I was really missing was the camaraderie. So when Halo came out for the PC, I stood and watched over some of their shoulders while they played. I was impressed by the graphics. Since I haven't ever played any other FPSs, I can't compare the graphics, but I like how Halo looks. Since I knew that the guys were having a lot of fun, I got off my soapbox and installed Halo on my machine.
I have to say, I have a lot of fun. There's something satisfying about running people over with a warthog, or sending them flying with a plasma grenade. But I imagine that it wouldn't be half as fun against AI players. The laughter and cries of dismay from the other players are something that you can't replicate in a bot game. And AI teammates can't strategize with you.
So I've pretty much given up my disapproval of FPSs. It's a game. It's not real. They have ratings just like movies, so that parents can actually be parents and decide if they want their kids playing it. Games are not the problem. Hands off parents are.