If you're not a confirmed Trekkie - then it's great! Excellent effects that have been pushed beyond all previously known limits, brilliant storyline, some great action and would keep you captivated the whole way through. My husband is not a Trekkie but enjoyed the film immensely and is now planning to watch some of the originals, so great was his enjoyment. No prior knowledge of the series is needed, as Abrams quickly and smoothly recaps everything you need to know without detracting from the film itself.
If you're a die-hard Trekkie, then it's a good film, but initially you find yourself making the inevitable comparisons between the old and the new. The "new" characters have kept the ethos of the old, but they're not the same and Trek fans may have a problem adjusting to that. I found after about twenty minutes, though, that I could ignore that and settle into to enjoy the film.
Special mention must go to the explanations into the characters of Spock the bullied and Kirk the rebel - I found that very thought provoking and saved me having to keep explaining bits to my husband.
The way Nimoy is introduced is well worth watching out for - it seemed to tie the entire film together. The new actors gelled well together and it was hard to believe this was their first outing as Trekkers. I hope that if there is a sequel, they will keep this combination of cast. It worked. It's left open, as any good franchise is, for sequels, so here's hoping.
In summation, then - once you get over the difference in characters - fantastic. Waiting for the next one