well, if that doesn't solve the problem, the problem my be in your cpu/ram.
If the game crashes (but not your computer) you may need to a) increase the voltage on your RAM, or b) need to loosen the timings on it. I had to up my voltage from 2.7v to 2.8v to keep my RAM at 400Mhz 2-3-3-11.
If you get hard reboots, you may need to increase voltage to your cpu. (this is an unlikley problem unless you're overclocking. )
I think they AI isn't half bad...some of the monsters, like the spiders and the zombies, are programmed to be that way, but otherwise I'd say they're relatively intellegent. Enemy Marines surround you and take cover, granted it doesn't have the appearance of super intellegnce as Hl1 did, but it is no easier.