Currently playing the beta. It's got a few issues, but this is surprisingly stable for a beta. Honestly, I've seen games less stable than this at full release.
It sucks that very few people got a beta key from the PcGamer giveaway because spambots grabbed them.
One issue I have is the balance with the zeds. The Skrake seems far too similar to the Fleshpound, and the Patriarch is too difficult. Also, you can glitch the patriarch by funneling him toward a welded door, have a person hold the weld, then have another person go around and shoot him. He'll continue to attack the welded door irrespective of how much damage he seems to take.
Oh, and there seems to be no purpose in the sprint feature. The original game didn't have it, and you have infinite sprint; so why have it at all? It just seems to be another button that I have to hit to get anywhere, which is particularly annoying because you can't map a button to capslock, because capslock is hard-mapped as voice chat. So I'm constantly hitting it by accident, and transmitting complete silence.
The slow-mo, lighting, and gore effects are utterly beautiful.