I wish they'd cast Benedict Cumberbatch in the role someone who may look nothing like Nimoy but could at least bring a little of the mystery and wonder of Spock back, with just a little darkness. Quinto plays Spock as a passive-aggressive human.
I think it's more a matter of how the role is written and directed than who they cast. Most likely Quinto is playing Spock the way Abrams wanted him to.
The only thing that bothered me about Simon Pegg is that he seems to be playing not Scotty from Star Trek but the over-the-top parody of Scotty featured in every Star Trek parody ever made.
Pegg's Scotty really does seem like a fanboy just getting the biggest kick ever out of Doing Scotty. Which is not without its charm, but...