Alright, I just came home from the movie. I know these reviews are a dime a dozen from fans at this point but I just had to type this now. I gave the movie an A; thoroughly enjoyed it, even after knowing spoilers.
The film, in many ways, seems to be about two things: the growth of the crew and revenge versus principle. From the beginning, it seemed to me that the crew members of the Enterprise are still getting used to each other, and are definitely adjusting to Kirk's command style. But we see them each mature in a situation where they're quickly thrown into a maelstrom that, frankly, they aren't supposed to escape from.
Starfleet has also changed since the events of the last film. That's probably my favorite part of the movie: the fact that Starfleet, and the Federation by extension, is still dealing with the fallout of Vulcan's destruction. Yet, it takes additional attacks on Earth to really give Admiral Marcus what he wants: the provocation for war with the Klingons.
It's no surprise that Kirk is willing to go out and get Harrison, but Scotty, who I see as a stand in for the audience, asks a question we've been debating on this board for years: "I thought we were explorers?" That quest from soldiers back to explorers, I think, forms the heart of the film. (Now I've always been of the opinion that Starfleet is BOTH the military AND an exploration organization, but in this film it seems the fleet is close to going into a more militarized direction.)
Kirk dying for his ship shows just how far he's come: at that point, he realizes that he IS going to lose someone from his crew, namely himself. He saves an Enterprise that is almost a mirror of him and the crew: broken, near death, desperate for a miracle.
The film's theme of revenge shows up several times: Starfleet's tactics in the hunt for Harrison, and Spock's chase of Khan at the end, in which he nearly kills him (and that stunned me. I knew about the fight, but the brutality of it at the end still surprised me). But, again, revenge turns into something more positive, as Uhura gets Spock to stop his beating of Khan and use him to save the captain's life.
This was the movie we needed after the first one. The fallout of the events of the first movie are dealt with here, and the crew is getting closer to the experienced, well-oiled machine that we know so well. Here's to the Five Year Mission!