I think that Tom Cruise can only act as well as the part is written for him. The charactor was well developed and Cameron Diaz was great. I did notice that both looked a litte "aged" but took nothing away from the movie.
It could have been better. Why do writers, producers and directors think that if you throw a little sexuality in the mix, that it will make a bad script better? Shia LaBeouf is a better actor than they gave him credit for and the way they developed his charactor is an insult to his ability to portray a more well founded role.
Movie was great and lead to a whole host of other possiblities for future pilots and films.
I think they got Bones and Spock dead on. Scotty was an improvement, but I don't like the way they cheapened Ohura. She had a lot more class in the original, but Michelle Nicholas was ahead of her time and it would take an exceptional actress to replace her.
As for Kirk, he was passable. William Shatner will always own the part.