It really depends a lot on what kind of game it is. A fighting game with 2 characters on the screen at all times in an environment can have much more polys per character/environment than, say, a First-Person or Third-Person shooter with lots of enemies and stuff.

Half-Life 2 is probably the most recent benchmark to guage with FPSs. Their characters were between 3-8,000 polys each, depending on importance.

We're doing a Real-Time Strategy game (Starcraft-type game) and our units have to be between 100-650 polys each depending on importance/size.