I highly recommend looking at some youtube gameplay videos. Originally I was about to give up on this but found that I just wasn't playing it "right."
Take a look at some vids, give it another shot, try different weapons (hint, the sniper is awesome for thinning out the herd before you rush in), and always keep moving. Move, move, move.
This game to me is like Robotron 2084 (2D arcade game from 1984) that is done in 3D. You cannot stop moving, you are constantly being surrounded.
Hope you get a chance to sink your teeth into it.