All right... this is definitely an interesting one....
I think this one has a really strong and poppy colour palette and a great logo, like colour-wise it feels very cohesive, and it has some really clean execution and a strong visual identity. The artstyle is a little oldskool, but the modern colours and clean digital lineart kinda make it work and feel like an homage to 70s/80s manga rather than just feeling old.
The main problem with this cover is it's trying to do way too many things.
There are people in the foreground who look like they're posing for a photo... but one of them looks scared of something off-camera down to the bottom left (because that's where they're looking), then one of them is looking at us while...smelling the person in the middle person's hair?
And then in the background we have one character looking star-struck while dramatically leaping to reach the hand of another person clinging tightly around a bemused looking character...and then you notice that the leaping character has... another tiny head...on top of his head?
I feel like you perhaps should have picked one scenario, like either, everyone is posing for a picture (maybe some are goofing off while posing, but they're all still stood or sat like they're having a picture taken) OR everyone is reacting to this dramatic reaching out between two characters. Or perhaps a scenario that more clearly gets across what the novel is about... like what if they were all on the bridge of a space ship, like a pastiche of Star Trek, but some of them are goofing off... or what if it looked like one of those team photos of astronauts, but some of them look kinda goofy? (actually now I look at photos of Astronauts... the actual real astronauts are pretty goofy. I have to share this one of the ISS crew).
(I actually really like how this photo takes advantage of zero G to create a fun composition, with the astronauts all arranged with their heads pointing in, and the little stuffed toys floating around, it's really cute!)
Because all you really need to communicate here is: DORKY FRIENDS. IN SPAAAAAACE-!
So keep your composition simple. It doesn't need to tell a complicated story, just focus on "friends" "silly/dysfunctional" "space"/"spaceship" and also... if the number of characters is an issue, cut down how many feature on the banner to the most key ones. It may even be worth considering putting just 1-3 characters and a space ship or a planet on there. If you do have lots of characters though, try to keep everything else simple, so they're not all vying for attention and pulling the viewer in different directions.
It's a different shape and sometimes complexity level/size, but you still might find the examples and resources I've collected on this Pinterest board where I put really great covers and a couple of cover composition tutorials handy!