I went in with no particular expectations. I'd not gone out of my way to read any descriptions of the movie, so I didn't know a whole lot other than that it existed and was going to have an all-new TOS cast.
1. They weren't kidding when they said "reboot." It was not hyperbole. o.O
On the pro side, people who have never seen any Star Trek before will probably enjoy this movie quite a lot - especially the next generation down. It's a good pilot-type story for introducing new characters and setting. The rebooted characters have just enough development on them to get things started, and now that they have license to pretty much ignore everything that happened after Enterprise, they can basically go anywhere they want with it.
On the con side (the retcon side?), I kind of liked what was there before....
2. People who have read a lot of Star Trek TOS Pocketbook novels may be at a disadvantage for enjoying the movie, especially if they read and liked Enterprise: The First Adventure, Final Frontier (the book by Diane Carey, not the movie), and Kobayashi Maru. The story the movie tells bears no relation to what the books say. On the other hand, the books are technically non-canon, so it's not exactly an arguable point. (Except possibly to argue against reading media tie-in novels, ever - but then you'd miss out on a lot of great stories.)
On the other hand, those who haven't read any of the novels may not like the discrepancies and total departures from previous canon either, so maybe I'm not saying anything useful here.
3. Apparently they decided to aim for comedy. Unfortunately, the villain was kind of cardboard as a result, and there were some plot holes big enough to drive a starship through. Also, the impact that should've been there for *mumble mumble* (!) and *mumble mumble mumble* (T.T) was decidedly nerfed.
That's all I should probably say about it at the moment. I might do a more detailed post later, when more people have seen the movie and I can stop worrying about spoilers. My reaction overall: mixed.
On another note, I was the only one who dressed up for the occasion (finally got an excuse to wear my Spock shirt!), and everybody looked at me funny. This town has no clue how to do geek properly. T.T