I wouldn't say "turned against" but Guardians did humor, character, and catharthis better than Avengers and Winter Soldier did action, intrigue, and story better. The lesson if anything is Marvel movies by and large seem to be getting better. Not a bad thing.
Winter Soldier did more story and intrigue, but it was not all that successful at them. It felt like they welded a hackneyed political thriller onto a solid superhero movie.
I'd say Iron Man 3 is the high water mark for plots in Marvel movies (though I have not seen Guardians).