I can't speak for the long-running fans, but I think JJ Abrams has done a good job of entertaining people who aren't familiar with the Trek francshise. I walked into the first movie without having seen a single episode or movie from the old days (apart from one movie involving dolphins, and didn't really *get* it) and thought, "that's a cool way to spend a Saturday afternoon."
I can understand why Trekkies might be upset at it being dumbed down for the masses, but it's quite the spectacle. Part of me wishes it would fill in some plot holes and go further down the character- or plot-driven routes, but then I do like harder SF (maybe the original Trek would appeal to me after all then...?). It's hard to tell whether it was intended to rival the originals, or do its own thing. I'm interested to see where the next one goes.
The casting is good, if nothing else. Zoe Saldana was damn cool, Benedict Cumberbatch is a great villain, and Simon Pegg never fails to make me smile (even if his accent drifted a bit).