LAG will hurt any online game really, especially First Person Shooters that require precision timing and aiming for an enjoyable online experience.
I am a proud owner of an xbox360 and here's my food for though:
Halo 3: This game is a good one however the constant lag and mic issues I have plague me to no end. In one game, I will be playing fine with a friend, no lag, mic is clear no problems, however in the next game, I can't hear him and he can't hear me. It got my frustrated to the point where I just turned off the game. (how out of the ordinary!)
CoD4: Good Game, however I only play it on the Hardcore settings. I cannot stand playing the regular matches where it takes emptying a full clip of the ak47(just an example) into someones chest in order for them to die. Other than that, its a solid game in which I receive very few occurrences of LAG. (im rank 14 or something in Prestige level 1)
Rainbow Six Vegas 2: Probably my favorite online game, however frustrating, its more challenging that the previous two. I'm a big fan of tactical / realistic shooters and maybe thats why this draws me in so much. When you have a shitty host though, it sure sucks the fun out of it!
Ace Combat 6: The thing that pisses me off the most about this game is the fact that it is next to impossible to invite a friend into a game! Error connecting to host...has appeared on my screen when trying to play with a friend way too many times for any piece of technology these days. That and the QAAM's are the cheapest thing on earth (I speak from the offensive side of things, as its way too easy to shoot someone down with those)
NHL 08: Favorite sport game!!
Online team play is SO much fun, but again, if 1 player lags...it can be a burden to the entire team. The only other thing that bugs me about the game is when the puck hits your goalies chest, goes up into the air as he is scrambling to make the save, and falls into the net...often times pushed into by the goalie himself.
To top that though, I was playing today against the CPU for kicks. Shot the puck, nailed the goalie in the face and then ricocheted off a defensiveman trying to get the puck (who ran in to the goalie, doing a tripping / punching motion attempting to keep his balance) and it looked like he hit the puck in with his fist. I laughed and rejoiced as I had just scored :D
LegendX9 for anyone who wants to game(case sensitive)!!!!