I would definitely class myself as a Star Trek fan.. and particularly of the original series, which I have watched every episode of in the past. And while I can see that the writers and director JJ Abrams have taken some liberties with the continuity of the mythos and to some extent the philosophy of Star Trek, I can totally embrace what they've done with this movie and thought it was really very good.
The casting is, to my mind, genius... Quinto and Urban in particular, and to a lesser extent Pine, Pegg, really manage to embody the original characters perfectly... as do many of the supporting cast: Saldana; Cho; Yelchin etc. There are some great scenes where the characters play off each other, and the classic Star Trek lines are littered amongst some really great dialogue, which often times I found to be very funny. Cumberbatch is excellent as the film's bad guy, a ruthless killer whom we're even allowed to feel some sympathy for, and I also enjoyed Robocop Peter Weller's performance as Admiral Marcus.
It did surprise me that certain things were switched around from the original source material and there was a bigish change to the ending. However I thought the overall story was pretty good, and there was plenty of action, interspersed with good character development, so overall I enjoyed the movie a lot and I personally don't see a lot to gripe about.