Saw it this evening. I had fun, it gave some laughs, had some fun action sequences, and was interesting in some ways -- even had a few poignant moments. I mean, I can't say it's a movie that will dramatically haunt me or anything, but I enjoyed it.
Chris Pratt IMO nailed the role of Starlord (in addition to being pretty damn hot with his shirt off). He was kinda the glue that held it all together. you could definitely tell the "real" actors from not-so-real ones. Bradley Cooper as Rocket was okay enough but didn't stand out; Pratt was great; Saldana was as solid as always, even if playing a type of character she's done a few times in the past; Dave Batista was adequate, although his physique was far more memorable than his acting ability; Vin Diesel of course didn't have much script to work with but managed to change things up a lot.
There were a few veteran actors (John C. Reilly, Glenn Close, Benicio Del Toro) who got some lines but nothing really spectacular; anyone could have been cast in those parts, it was more a "freebie" role for them. Mike Rooker of course chewed up the scenery but he was playing the same sort of character he typically plays in anything I see him in. Djimon Hounsou played his part but was kind of just a passing face. Brolin was adequate but wasted as Thanos. While Lee Pace did fine as Ronan, he was just your typically baddie villain out to gain power and destroy the world, blah blah blah.
Two standouts -- Karen Gillan as Nebula and Christopher Fairbank as the broker. Gillan I'd recently seen in Oculus and she was damned good, so I expected to see more of her in upcoming films, and here she was, one of the more memorable characters in the movie... I hope her turn here opens some more doors for her. Fairbank just really brought a lot to the role despite not having much screen time, and I'll remember him.
The movie did have a few slight missteps -- typically when there was a serious beat and you weren't sure whether there would be a joke at the end (as it often did), and when it didn't, the serious tone kind of hung too long in the silence, so it was hard to know how to process it. There were also some serious moments that flowed just fine. There were even a few brief teary moments, including the end sequence.
There's of course an additional clip after ALL the credits have rolled. Hard to tell whether it's forecasting anything, but I was laughing pretty hard at that one since I'm old enough to recognize it.