@flolle In addition to what @rcartwright mentioned, I would work on the perspective. Your front-to-back angles are ok, but you pretty much have no perspective going up. All the vertical lines are parallel. Even at this angle of view, there should still be a bit of vertical perspective as you go up. Also, the image seems unnecessarily tilted, I assume for effect, but it isn't working here.
Not knowing the story, it is hard to comment on the images content, but might be good to zoom in on your characters a bit more, maybe even taking the view lower, and looking up at the characters slightly. Also, considering their proximity to each other, their greeting needs work. A like what the rabbit is doing, but the kid, realistically, would not be waving to the rabbit if he was that close. I would have the kid doing the same thing back to the rabbit, or maybe a high five.
I would work on the placement of the floating rocks. The one above the building would work better if moved to the right so we could see the point at the bottom. And the one in front of the ship should move tot he right of the longer laser/light so it does not look like the ship is shooting it.
Finally, from a design standpoint, your title needs to be much larger, stacking the words, and maybe making the "O" in "Core" the spot where the fragment graphic is placed.
Hope that helps!
