I saw it a bit ago at an advance screening and here's my kneejerk reaction:
Solid action movie, but not that great overall. I was very disappointed with how one dimensional Nero was (almost no character development whatsoever). I also thought the movie lacked any real substance beyond some basic Kirk-Spock friendship stuff. There was no real thematic exploration of the human condition or attempts to be culturally relevant via allegorical storytelling. In short, the basic goals of sci-fi and Star Trek were ignored, in my opinion.
There was a lot of good stuff. I love that JJ rebooted the trekverse via time travel so that he can (and did) do whatever he wants! That's the only way we can sense any of the characters are in any actual danger, which is awesome. The opening scene was freaking amazing. The comedy was mostly good, and not too cringe-inducing. It was EXTREMELY well cast (with the exception of Chekov).
Perhaps the best move JJ made was fundamentally changing Kirk and Spock's characters via previously unhappened deaths. The instant George Kirk died Chris Pine was playing a new character who grew up without any male role model - totally different from the Shatner's Kirk. Similarly, Quinto's Spock had to deal with a level of emotional trauma previously unknown by Nimoy's Spock. This really allowed the actors to create totally new characters so they wouldn't be compared to the old performances. Brilliant thinking, IMHO. Karl Urban should also be credited for nailing Kelley's McCoy down to the mannerisms.
My big disappointment was that the setup to fix the mistakes I previously outlined was there, but not taken advantage of. There was no exploration of the similarities between the losses Kirk, Spock and Nero faced, and why their reactions were different. The characters weren't even given a chance to understand that they lived, in many ways, very similar existences. After all, Nero said clearly that he wanted a "normal life" but that was taken away from him, while Kirk experienced the opposite - going from an extraordinary life to nearly living a normal life because of the death of his father. Spock, similarly, cannot live a normal life because of his mixed ancestry. Interesting parallels, with some key differences, and chances for empathy, bigger messages, etc. all lost because Nero, as a character, was nothing more than a shallow caricature of Khan.
And what was up with the last scene??? Kirk and Spock blowing Nero away flew in the face of the humanistic nature of Star Trek. I know they were angry, but one of the messages of Star Trek has always been putting aside differences, no matter how great they may be, so that peace has a chance to thrive. They could have had a very nice Balance of Terror-esque ending scene with Nero killing himself because he has no chance to win and he wants to reunite with his dead family in the Romulan afterlife, after talking with Kirk and Spock about how they are not so different and may have chosen the same path as Nero under different circumstances. Come on guys, that's Star Trek 101.
So, yeah, I have a longer review I'm saving for later this week, but that's my kneejerk. Good setup, lots of missed opportunities.
Sure, some people have made some asides about characterization and so forth, but mostly it's been along the lines of: The Kelvin blowing up is awesome! Vulcan blowing up is awesome! Kirk's father dying is awesome! Spock's mother dying is awesome! There's no more canon, so now anything can blow up and anyone can die! 
