The movie's plot is best described as a long series of short episodic adventures, only loosely related to each other in that they gradually pass the characters along the course of the main plot. This of course makes perfect sense if you look at the movie as a live-action comic book, with each weird mini-adventure being a different issue of the comic.
The movie has been criticized for showing glimpses of fantastic alien realms, hinting that the characters will adventure there and then just zooming past them while the plot becomes more conventional. This is valid, but a quick montage near the end shows the Pearls have been observing and interacting with those realms and taking aspects of them to build their spaceship. This makes the little parts we see in the movie into Chekov's Guns from their point of view, which pay off when they achieve their aim.
Simple, but in the introduction when they're meeting the various alien species, why do they all shake hands? Because they can recognize that it's a gesture of peace.
There has been criticism of how Rihanna (in human form) delivers her line in almost monotone, but while that may be a case of weird performance, it's perfectly in-character for Bubbles. She is one of the Starfish Aliens, she can sure look human, but it's one thing to mimic appearance and stock poses (that her job demands) and completely different to mimic emotions and expressions of a species that's biologically 100% different from your own.
Fridge Horror:
No one ever disputes the Commander's predictions about what will happen to the human empire if the true story of planet Mul gets out. For all we know, humanity will be ostracized from galactic civilization and lose the benefits of life in Alpha, or unless that the other races will forgive them due to the fact that they will revealed the accident and that it was Commander Filitt's fault, not the humans'. In fact, in the comic that the film's story is (very loosely) based on, humans do get kicked out from the station for a hundred years for a transgression.
The Boullan-Bathor evidently have no problem with eating sentient species, and routinely drop "fishing lines" into the Red Zone where nobody's supposed to go. Who actually does hang around down there? The Pearls. Sure, those "fishermen" could have been trolling for lizards, but given the Pearls' appreciation for beauty, it seems entirely plausible that the Boullan-Bathor have snared a few of them, too.
Also, if a live human head with lemon is a prized Boullan-Bathor luncheon, what other sentient "ingredients" may have gone into all those dishes the Emperor was rejecting?
The various habitats that Valerian bashed his way through could have incredible consequences from the breaches.
Even Valerian is afraid of creating a diplomatic incident with the Boullan-Bathor. This implies that they are much more feared than the other habitats he passed through. This doesn't bode well for galactic civilization now that their emperor was killed in what could only be seen as a black-ops assassination.
