I also was in the alpha, but as a versus only player I saw nothing that excites me. Though we didn't see the PVP mode yet, and not all infected, just from the co-op it seemed to be more about avoiding/dealing damage than split-second tactical stuff. I'll look at PVP footage on the youtubez when it's out, but I'm not holding my breath for it being in the same ballpark.
That's not just because of the alpha, but also all that talk about "re-defining the genre they invented" but also "not repeating themselves". Originality is great, but if you invent action chess, and then go on to make snakes and ladders instead of improving on action chess, just to "not repeat yourself", that's silly, and that's the vibe I'm getting by now... they may not even know what they had.
Anyway, if it has a *lower* skill ceiling than L4D, people might easily still play versus long after WB decided running B4B servers is no longer profitable enough. I'd love to be proven wrong, but we'll see.