I think, physically, Quinto works just fine as Spock. In fact, as far as looks go, he is an inspired choice.
Acting is a different matter entirely though. One of the great things about Nimoy as Spock is that he always totally sold the role. Even in the most silly and ridiculuous episodes, Spock was consistent. He was a rock. He reacted to every situation in the way that the most composed and dignified Vulcan would. Nimoy was a fucking incredible artist, I don't care what anyone says.
I think the new movie's success(in the mind of me, FWIW) depends far more on Quinto's performance than anyone else in the cast. I sincerely hope he's up to the challenge.