Summary: It rocked. Not perfect, but it rocked.
The most important thing I can say is, avoid preconceptions. As they've said, this isn't your father's Star Trek -- it manages to be respectful of the original (moreso than I was expecting, in fact), but this is a full-blooded reboot of the story. (I want to talk about it lots more, but for now I'm avoiding spoilers.)
Casting and acting were both excellent, much better than I was expecting. Pretty much everybody captures their characters well. (*Especially* Bones McCoy, who is pitch-perfect.)
I will warn that this film is a serious example of modern shaky-cam: both the story and the cinematography are downright frenetic. It's fun and fast and energetic, but you can get pretty dizzy. This is an Action Movie Dammit.
I will also warn that you'll need a good-sized dollop of suspension of disbelief, in several respects, not least the backstory. I suspect that the backstory will be a bit "huh?" to the average watcher -- it kind of comes out of left field. If you want to really understand what led up to this, I commend Star Trek: Countdown, a four-issue comic book that came out (rather quietly) over the past several months, which is the prequel to the movie. It's not a great story, but the movie leads directly from it -- the opening of the movie follows almost directly from the last page of the comic. It's not essential -- the backstory *is* recapped -- but the comic fleshes out the very brief and slightly cryptic recap.
It is *well* worth seeing at the Jordan's IMAX: this film benefits from both the huge screen and huge sound. (And comfy seats.) It's the first time I've ever seen Star Trek truly envisioned as a modern blockbuster, and they pull out every stop. It'll be there for the next two weeks -- get there if you can.
Anyway -- go see it. They're shaking the franchise to its core, but this is a worthy restart: I find myself actively interested in seeing the next one...