In a word, brilliant! Don't think twice about seeing this, there's something for absolutely everyone here.
I 100% buy the new cast as the old characters. Chris Pine is so good as Kirk, he's the new cocky young hero for a new generation. I loved the scenes with him and Karl Urban as McCoy. They ARE Kirk and McCoy, and that frienRABhip was great to see. Then you've got Zach Quinto doing a mesmerising job as young Spock. Pitch perfect performance, and showing more layers than Spock has ever had before. Special mention should go to Zoe Saldana as Uhura. This girl is way talented and should be a huge star by now. It's her time right now! Great chemistry with both Kirk and, er, someone else who I won't mention because it's a bit spoilery!
The action and CG is second to none. It's all done in the more modern style of insane closeups and shakey cam, but that just makes for more of a mad ride, and you're in no danger of thinking of it as a TV show. That was probably Abrams's aim from the start. This is definitely the most filmic Trek ever.