You just have to get used to the flow of the game. If you'd spent a fair bit of time punching guys out in stock Doom back in the day, you should be fine with this. It's roughly the same mechanic, you've just got other guys who also punch and you've got weapons that break and can be picked up, thrown, etc. I was playing on the second to hardest difficulty and doing pretty well with it.
What I think is really remarkable is how cohesive and consistent the art style is. It looks like a Doom game, but at the same time it totally doesn't. I get a real Duke3D feeling when I'm playing it, in some ways. It's really neat.