I can't believe that no one else mentioned the bit about "pour walnuts over your shoulders and shampoo with BARBEQUE SAUCE!" Hardest I've laughed at a ZP review for a while.
As to the substance of the review, I think he is pretty reasonable in his assessment, althought I would have thought he would've given them more praise for essentially pioneering a required co-op element. I cannot think of another non-team game where you can't either run off from your teammates or kill them, and still have a reasonable chance of solo success. It's a very subtle point, but it's there. Combine that with an element that not only does not reward but actually penalizes the slow, methodical player-- unlike almost every other FPS out there-- I felt L4D was, in fact, very refreshing and innovative. Furthermore, as Yahtzee pointed out, the ability to interact with your friends in a simulated crisis situation (just FYI: make sure you use 'open mike' and not 'push to talk' voice comm), and...
Well, there you go: in a single paragraph, three ways that Left 4 Dead is not only very well executed, but substantially refreshing. More than I can say about most games these days.