I wasn't a fan of far cry 2, I like my stealth and strategy, but I never really found that planning an assualt was much better than not. I guess the AI was ok, not great, they just seemed to slowly crowd around you.
I've no idea why people said Dead Space, they're zombies, they either walk or run towards you. Nice atmosphere though.(That wasn't a pun)
In Left4Dead the AI is there for you. Which is sometimes annoying, but works well. I wouldn't say the enemies work together.

All I can remember of Fear is going into slo-mo and the enemies pushing cupboards and things over for cover, smart asses. Is there a Fear 2 out soon/now?

Its a tough question though. Nice graphics, special abilities and things usually cover up poor AI that just runs at you or just hides and takes potshots.