Christopher Bird’s review published on Letterboxd :
When I discussed both ANT-MAN and DOCTOR STRANGE, the common thread in each of those films (along with IRON MAN 2, INCREDIBLE HULK and other "lesser" Marvel films) is that they aren't really about anything other than their plots, or at least (in the case of decent-but-disposable entertainments like ANT-MAN and STRANGE) that their themes aren't communicated strongly enough to really give the films impact.
GUARDIANS OF THE GALAXY doesn't have that problem: it knows what it is and handles its core ideas (a boy who's been running away from the death of his mother finally confronts mortality and responsibility; losers and outlaws band together for the greater good) effectively and efficiently. Chris Pratt's performance really sells this; he puts in a lot of fine detail work, a lot of subtleties of glance and jaw, to convey his internal transition from ne'er-do-well overgrown adolescent to realized adult. It's really something to see, all the moreso because he's not laying it on thickly at all - he's letting the small moments in between the gags and fights carry his emotional transition.
All of this is to say: it's a good movie. Pratt's performance is the most important, but Zoe Saldana, Dave Bautista, Michael Rooker, Karen Gillan, and John C. Reilly all contribute good work, and Bradley Cooper and Vin Diesel give excellent vocal performances, so overall the ensemble is strong. (Lee Pace is mostly a bad-guy cipher as Ronan and Glenn Close seems mostly bored, but the movie can get by without them giving A-level work - and it manages to mostly get past the dreadfully dull Thanos interlude.)
Furthermore, like all of the good Marvel movies, it has a strong visual sense, particularly with respect to its locations; it's really very funny; and it has a sense of personal style, which most Marvel movies only have in small amounts.
It might not be fine wine, but it's a damn good cup of coffee.