(edit: most of this message doesn't make sense now, since the first post at first had concept art which is now deleted)
I'd rather call that concept art, but even so the rules here do say that forum threads for games/projects with only mockups (or just story or the like) aren't allowed, you gotta have some actual proof that the game is properly real with screenshots or videos. Plus your concepts being from 2021 doesn't uh... give much hope either.
Tho for the time being I'll first comment that Zones 1, 4, 5, 6 and 7 seem to have veeery similiar style for the top of the foreground, sure colors and such will change things up but even in sketching and planning phase I recommend thinkin of some variety. Also a shame the logo you shared here isn't as stylized as what you had sketched on paper.
As for the project overall, guess there's muuuch to ask about since you didn't share anything really and I'm curious. Guessin it's 2D and genesis-styled due to the framework you use, but what playable characters are you thinkin of? How's the game structured? Got a story in mind? How will the name "Nebula" take part in this, are things happening in space?