The film feels like three main acts. There's a "Hey, the gang's all here." act, the real story/plot/mystery/movement act, and the final third act which for me, killed the vibe of the film and made it less about originality, and more about homage.
Let me explain.
The first act: JJ Abrams brings the great cast together again from the first film. And what I mean is this: Everybody feels like they've been together for as long as the timeline in the film has passed (a year since the first film if I recall correctly). There's a great vibe with everyone like they're family, a concept that comes up often during the film. All good here. Like returning to your favorite characters, it's nice to see everyone again.
The second act: Mystery, terrorism, action and the introduction of other parts of the Star Trek universe (Hello, Klingons) and of course the main protagonist, John Harrison. Benedict Cumberbatch, who I've never seen in action before, is excellent as Harrison and demands the screen whenever it's pointed at him. His character is the one you take the real journey with — in fact, I found myself on his side more so than the ones we're supposed to be rooting for. Anyway, good and fun storytelling here.
The final act: Here's where those Abrams-Spielberg comparisons start to make a bit more sense. Abrams is not as heavy-handed (yet) but the final act, where we learn that yes, Harrison is actually Khan, killed the film for me. As soon as I discovered this fact, and if you know The Wrath of Khan, then you know how this film starts to end.
Abrams does a solid and reverses the sacrifice, but then goes to great lengths in extending the movie on and on, and you begin to think, "Huh, this feels a little long." Once you've made that connection, the illusion, the movie magic, it falters and fades.
The film ties up all too neatly with a happy ending for everyone which I felt was a bit of a cop-out. The Wrath of Khan had more balls. And I wish Abrams did too.
In general, I'd watch it again for the first two-thirds, but it's that last third when I'll snap out of it again and remember that it's just a movie.