I played a couple of rounds yesterday and had a lot of fun. The pace is slow with sound being the primary source of awareness, aiming is difficult and reload takes ages. You progress slowly while heavily relying on your teammates. Zombies can be dangerous as they seem to be stupid and unaware at first and then, bam!, they start rushing at you fast so you fight for your life and make a lot of noise which is heard throughout the map and attracts other players. PvP encounters I had were all one-shot-kill (with possibility of being revived by teammates unless they finish you, for example, by burning your body). My first game ended quickly as I was wading some swamp and a monster straight out of Lovecraft's deepest dreams finished me off in a blink (not revivable). The next two rounds were more lucky (being careful is paramount), as I got some player kills (1 and 2, IIRC) and extracted both times successfully after killing the Butcher (boss).
We'll play more tonight. For me, the game is well worth the money. If they continue support after launch (another map, modes, weapons, etc.), it might have a potential to live on. My only problem so far is graphics. Cryengine sucks, textures load too late (even from SSD) and resolution isn't great. But it's just an aesthetic problem because for me because of the way I play shooters (very close to a big screen). You don't need to spot enemies far away because you'll hear them much earlier. Also, due to thick vegetation and the fact that most focus points are inside buildings, you mostly fight close quarters. Additionally, the mechanics (difficult aiming, iron sights only) don't allow for quick scoping and similar techniques.
I think this new PvP/PvE/BR mix sub-genre is something I'd like to see more in next gen shooters, especially with new hardware sound capabilities. The only other game which I know of that has similar mechanics is Escape from Tarkov, which I cannot really enjoy as it's virtually impossible to play with a joypad.