The first thing that comes to mind is that, unlike the first GotG film, the sequel has lost the ability to get its act together. Sure, the first Guardians of the Galaxy was far from being a "serious" superhero movie (maybe because having Iron Man and Captain America battle each other is serious enough for the Marvel universe), but at least it could, when the circumstances demanded, be mature and even touching, the "we are Groot" moment being a perfect example. That contrast deepens the experience, making you care about what's going on ever so more.
This film, however, feels as if, with Groot reduced to a twig childhood state, the same happened to the brains of the other characters: now they are constantly risking the lives of their own and their friends' simply to pester their sense of masculinity or for the sake of unhealthy banter, only to end up with some turd jokes. There are a few glimpses of maturity here and there, but when yet another film with Kurt Russell and Vin Diesel tries to build all its pathos upon the "we're family" line, it becomes just too much to handle.
Another thing that strikes you about GotG2 is how all over the place it is. The Marvel universe is seriously lacking villains right now. And if the Avengers can afford to simply fight each other in the absence of a better thing to do, the Guardians have to be supplied with a multitude of strangely generic or single-use baddies, especially since the family values doctrine demands some old baddies to become goodies. The vindictive golden lady might have been mildly amusing if her plot line was put in here for jokes only, but the ending credits scene shows otherwise, so it's not even funny anymore. And the figure of Peter's father, despite all its technical grandiosity, ends up kinda hollow inside (in all senses). So even when the good (or should we say infantile and aggravating?) prevails, there's no true satisfaction in it.
Finally, there's this weird glossy neon atmosphere all around this film. Everything is polished and sparkling and blinking with a million different colors. In that sense, GotG2 definitely takes after Doctor Strange: both films, despite all their potential, look like some generic Japanese/Korean action RPG game: too fast-paced, too jerky and, most of the time, too meaningless. Maybe the overabundance of shiny objects and slapstick jokes was meant to hide that lack of essence the films fail to admit.
All in all, I take GotG2 as a sign of geriatric dementia for the whole Marvel universe. True, the style and the looks are still there, but when it comes to charting course forward, there seem to be no true aim ahead, and, most importantly, no true understanding of why such aim should exist in the first place. This makes the Guardians franchise not just the "style over substance" type, but simply pointless.