Actual dialogue from this movie:
"Put it down, you fool, or you'll destroy us all!"
"You're scared because you're soft!" [Pounds chest] "In here!"
"The time has come for you to renounce your paltry gods" (bonus: mangled pronunciation makes it sound more like "poultry gods")
[Hero miraculously survives] "But you're mortal! How?!"
There's an old bit about how the difference between amateur clowns and professional clowns is that the professionals will never paint their entire faces. Too much expression comes from the area around the mouth; obscuring it is unnatural. If the clown's goal is to look recognizably human and not, say, creepy, they know that restraint is sometimes appropriate. Attention to detail is a sign of professionalism and care about one's metier. If people think those details don't really matter, and you should just have fun and enjoy it, well, that's a vote in favor of creepy clowns.
The dialogue above is a representative sample and not nearly exhaustive. Nobody paid much attention to the details for this movie. Had they done so, there would not have been an incomprehensible rush of names at the beginning, that eventually resolved itself into a proposed genocide of one people by the representative of another for violating (maybe?) a peace treaty whose terms and purposes were not well-established, despite far too many Phanton Menace-lite scenes of diplomatic negotiation. There was also an Infinity Stone, not that the movie told its viewer anything about it other than it had a lot of power and maybe could only be harnessed by certain types of beings. As with all the other Marvel Cinematic Universe movies, there is no clear metaphysics, or physics, or economy, or politics, which all great science-fiction movies--even all the good ones--manage to establish. The sequels to Guardians have already been announced, lest the viewer be concerned someone might die: all the important characters will stick around for another two movies, no matter how 'dead' the viewer is to believe they are 70% of the way through the film.*
There are also the political complaints: a multi-ethnic, multi-species group of heroes led by a white man.** Four women characters in total: a dead mother, who lied about the main character's father's identity; the appropriate-for-a-13-year-old 'love interest,' who is just a female man except when she inexplicably isn't able to fight for herself and needs to be saved; a slave; one of the clear bad guys.
Drax has some generic "you killed my family" backstory that is delivered entirely in dialogue, without any useful details. It's as though no one thought to do the Gladiator-style flashback, which requires no actual action sequences and takes up perhaps five minutes. Everyone else in the group goes along for the ride for reasons that are never made clear, or quickly abandoned. There's also no character development, a rising problem in science fiction and comic book movies. No one has even the most basic of character conflicts: no one has to make any difficult choice, never mind being troubled by the conscience of a Mystique or Nightcrawler. Has any character learned any lesson aside from, perhaps, "believe in yourself" or "trust in your team"?
And this leaves aside the question of whether this is a worthwhile type of movie to be making in the first place, but what it sets out to do, it does poorly. Why was it so successful? Why is it so well-regarded? Because it was explicitly not as gloom-filled as many other MCU and science fiction movies.
*I am not dumb. If someone is "dead" and the movie has an hour left, they are not dead. If Agent Coulson wasn't dead, ain't nobody in any Marvel movie ever going to be dead. So that's some metaphysics, at least.
**Professor X might run the X-Men, but he clearly has some ambivalence about it.