[Small spoilers]
See, my problem is that so many films are trying to either shove weighty gravitas down our throats to reflect how sucky our society is or whatever, or they're trying to blind us with flashy CGI. Guardians does deliver on the effects, but I thought the characters were more interesting on some levels than their Avengers counterparts. When the film takes a turn towards the tragic, it has a much stronger impact than the "scheduled downbeats" that you see in other superhero films. The characters in Avengers, the Dark Knight trilogy and X-Men have epic-level problems; they live in a grandiose world where everything is either political or greek tragedy, but the Guardians have more relatable issues and I found them to be more sympathetic and perhaps more touching than anything else I've seen in superhero movies. When Rocket goes into his sad drunk speech, you get where he's coming from and you genuinely feel that he's in pain, and Quill's obsession with 70's music becomes more understandable when you know his backstory. I think the fact that the actors took their work very seriously made their characters more human, and maybe they needed to be given the alien nature of the cast.
That said, Guardians still delivers on the fun, without societal or political commentary but with a very human set of characters that you want to root for, and maybe that's its greatest strength. It may not be on the complex level of its competitors, but it has more heart.
[Edit]
I want Rocket as my wingman!
