... although my wife and I had thought it was a preview of the whole movie until we were sitting in the IMAX.
I'm not familiar with the comics or characters so my impressions probably don't count for very much, but FWIW and making some effort at avoiding spoilers:
* the preview began with the director speaking to camera, basically hoping we enjoyed the show, followed by a quick intro. to the main characters, followed by a big, complicated action set-piece, then a short outro.
* the audience seemed pumped at the start and there were several real laughs, though that lame "what a bunch of a-holes" line you've heard in the trailer was met by the sound of crickets and perhaps a rustling tumbleweed
* the giant plant monster seems like a cool dude, the raccoon is evidently the brains of the operation and Chris Pratt's character is fun, though likely to suffer in comparison to his killer goofball delivery as Andy Dwyer
* the 3D effects worked fine sometimes and, perhaps inevitably, other times just made it hard to tell what was happening on screen
* the audience seemed kinda happy with what they saw, but there was a general feeling of minor let-down. To be fair, it's possible that many others in the audience hadn't realized what they were signing up for and were expecting more than just a 17 minute excerpt.