I thought it was decidedly average. The plot and special effects were fine but once we are told who and what John Harrison was it started becoming a drinking game to see how many old-Trek references you could fit into the movie.
It kinda felt like Iron Man 2; the really good bits didn't last very long and they were on the trailer anyway.
Leonard Nimoy's cameo was silly. "I told you I wouldn't say anything about Khan. But let me just tell you about him." It also highlighted the flaws that seem to crop up in Abrams' movies; stuff doesn't work unless it needs to. They can't communicate with Kirk on the Vengeance, lose track of Harrison who is only a few hundred metres from the ship and yet they're able to place a direct call to New Vulcan?
The ship sizes are all over the place. Enterprise is still huge. Vengeance is even bigger. And yet the port Kirk and Khan aim for is on deck 13. Which is halfway up the engineering hull. So basically the Vengeance is the size of Voyager.
Also, they're clearly in lunar orbit (an establishing shot shot the Earth clearly in the background, at least 350,000km away) and all of a sudden they jump Lagrangian points and are now in a deep gravity well...
It was ok but had it's flaws. The ending was very weak.