Funny thing is I never took Star Trek seriously because it always looked ridiculous and campy with low production values. My wife got me into it several years back and now I'm pretty hardcore and have watched back through all of the series and movies.
Coming from the perspective of someone who notices when the eff up details of stuff like this, I've gotta say the movie was incredible. I can see why it would be awesome to non-Trek fans, but for him to be able to capture that as well as appeal to the old fans... that's skill. I was amazed.
Some fans like to nit-pick about the casting, but I personally thought it was great over all. Things that were inherent to the original characters were brought out very strongly. Most of the actors looked the parts very well, 'cept Scotty a little and the fact that Chekov doesn't look anything like the original... like as far away from it as possible. However, I could overlook that because the guy who played him nailed Chekov as a character so well.
I also think the alternate timeline thing is a great and creative way to bring new story and make it plausible for a change in the canon. Anything that happened after (SPOILER)Nero showed up at the very beginning and polluted the timeline could be written off as a result of that.
If I were going to pick one thing that didn't quite hold true to the original it would be that Sarek just didn't seem ashamed enough of Spock. I mean... all through TOS and notably in the films... Sarek was all but disgusted with Spock and never so emotional or human about him. Not that he's very emotional in this movie, but more than he should be.
I also thought the (SPOILER)Uhura and Spock thing was a little odd. Sure it doesn't necessarily fly in the face of any canon, but it's a little odd. The moment in the turbolift right after (SPOILER)Spock's mother died could have been an immensely touching moment, but both my wife and I were far too distracted by the awkwardness of her (SPOILER)kissing him. Perhaps that moment would've been better if they'd set up their (SPOILER)relationship a little better. The only hint at it prior to that was when ships were being assigned and the issue of potential favoritism came up. Too subtle to suddenly have (SPOILER)her making out with him, and mildly inappropriate how passionate it seemed considering his friggin' mom just died.