The AI in halo 2 is pretty smart, elites will run behind cover when im trying to gun them down with my turret, and wont come out until i stop firing for a while, and the second i start again, theyre back in, those flying dudes swarm around you, grunts are pretty convincing as the stupid-cannonfoddder they are, Jackals tend to stay in groups to maximize the power of their wrist shields.
I mean, the fact that a marine can drive you around the map in a warthog, or that 2 marines can fully use a warthog on their own, is pretty amazing.
Everytime i try to hide behind some cover, thee enemy will try to blast me out with nades, or sneak up on my ass and start beating on me.