I think Abrams is much better suited to Star Wars than to Star Trek. I liked his first Star Trek movie well enough, but the second one, not so much. It would have been better if they didn't attempt to use a villain that was done 100x better in 1982. In any case, neither were great Star Trek movies.
He admitted that he was not a Star Trek fan before he began working on the movies, and knew almost nothing about it, which translated into the spirit of what Star Trek is being almost completely absent from the films. Conversely, he grew up with Star Wars, and his style of direction is certainly better suited to it.
I expect that the movie will be mostly great. It'll almost certainly cleanse away some of the prequel filth from the overall franchise, but I'm not expecting it to be the completely mind-blowing return to form for Star Wars that some are expecting. I'll be happy to be wrong on that count. If I'm worried about anything, it's that I'm so far unconvinced about Rey being an adequately compelling protagonist, and I'm a bit concerned that they went overboard with the goofy roller droid beeping and squawking and clanking around all over the place lol how funny let's sell more toys! You're not going to out-R2 R2, so why bother? I hope JJ learned his lesson from Khan. Not even Benedict Crumblersnatch could save that character.