Finally watched this at GenCon. Solidly amusing. Not something I'd go out of my way to watch again or own, but if someone said, "Hey, let's sit down and watch this movie I happen to have on this television I always carry in my pocket," I'd say "Sure, okay." I laughed most of the way through.
I think it suffers from Comics Condensation Syndrome (comidensation, if you will) in that the first half of the movie is the first six to twelve issues of a comic series, establishing all the characters, and then we skip over about fifty issues, and the last half is the final six/twelve issues of the buildup/resolution of the overarching plot/villain/thing. It makes comics movies tend to feel disjointed, and this one particularly so, what with the half-dozen character backstories AND the whole concept of Thanos and Cosmic Cubes to explain. There's just kind of this hiccup and then suddenly they're all friends. Which I can get beyond because it's the premise of the movie, but it requires some mental effort on my part, y'know? I'm actively suspending my disbelief and it's putting a little strain on my back while I'm allegedly relaxing.