I just went with a standard "soldier" character this time around - I'm enjoying deploying my two (2!!) turrets, firing bullets and rockets each... There's a tech that allows them to produce a small nuclear blast later on as well!
Also, the enemies are awesome! When you encounter your first goliath, try shooting his helmet off and watch him go on a rampage
Also, midgets with shotguns riding behemoth-looking creatures is just pure hilarity
Oh, and the new PhysX effects are insane, turn it all the way up if you've got the hardware