It's not L4D. Completely different.
I had fun for a while with it, but never got far because the save mechanism and difficulty were extremely challenging and frustrating.
This was extremely annoying. You can only save in bathrooms or VERY rarely at the end of missions. Also, breakable weapons are INFURITATING. However, it's fun to kill zombies with a bowling ball, or a shower head, or a stack of CD's (although that one is hard to pull off).