Strictly speaking, 'Guardians of the Galaxy' works because it is the story of a child, who in order to overcome a terrible trauma (first five minutes of the first film) literally takes refuge in a fantasy world, with walkmans, raccoons and talking trees.
The second is fixated on a theme, that of the father, to be emancipated from or accepted, as every child must do when growing up. The third is the story works because it closes the circle, the child grows up and Gunn (à la Spielberg) tells us that to do so, there comes a time when melancholy must be left behind.
The film did not disappoint my expectations and I fully agree with your review.