I found Killing Floor to be a very weak compared to Left 4 Dead. The game has no real depth, as some design flaws and repetition really ruin the game. It's a shame because it could have easily been a competitor for Left 4 Dead, but it falls short.
I think the main reason why people praise Killing Floor is because it has more content than Left 4 Dead, yet it doesn't have the fun factor.
I hated the game so much I got a refund from Valve.
Plus, it has the most annoying voice overs in the history of gaming.