First the effects are amazing, both from the technical point of view and the artistic. You really do get the sense of a whole world that is only somewhat like ours.
The best analogy I can think of is Jupiter Rising, except it was done much better.
The basic plot does meander, several times the main characters veer to an area that had no effect on the main plot and does not tell you anything you have to know. This is done because the movie obviously values world building as much as it does plot. Despite this it does not and probably could not explain everything, or even most things.
For example it is never explained how Valerian could be a major with at least nine years of experience. It is implied at one point that they can put you in a box and de-age you but it is never said. The way the main characters are treated also implies this, their age is never remarked upon, they appear to be normal agents from how others interact with them. It could be that age is cosmetic, you are literally as young as you want to be.
The world that the movie builds is very large and complicated with a large amount of technology that is so far above us it might as well be magic. Trying to tell us what they all are and what they all do would not be practical.
Honestly the main problem I have with the movie is with the chemistry between the main characters, or the lack of it. It was established that Valerian does value his partner and would risk anything to save her just because she is his partner. At best it comes as more of a intellectual attraction then anything else.
When all is said and done however I just don’t think the whole romance sub plot was needed. The purpose of romance in such a movie is normally as a driver for the plot, to provide a reason for the characters to be moving in the directions they are moving. In this case it was not needed.
I would recommend that you see the movie if the art and world building look interesting. If you looking for a character piece or a logic puzzle then I would probably wait for it to come to Netflix.