Hello and welcome to the community!
I assume this is your first game? Well, space adventure is definitely a cool genre with lots of possibilities.
As far as your screenshots go, there is a lot you can improve.
The first screenshot just seems to be a bunch of scifi pack stuff thrown into the level editor. There is no rhyme or reason to any of it and it looks extremely non-sensical. You can start by actually making some terrain. Here is a basic tutorial
to make some relatively okay looking topography.
What is particularly bad about is, is that long row of rocks that form some sort of path, I'd really remove that entirely. Try to add some terrain structure to make this temple look less out of place and don't scatter random space props around on a flat terrain.
Now that first interior screenshot has the same problem, random assets scattered around. Here are som pointers:
1. The ceiling texture is really bad, I'd use something else entirely.
2. These incredibly 90s looking gas station bathroom stalls and toilets really don't belong into space
You can start editing your props texture to give things your own style and look using free tools like gimp or paint.net. (photoshop and paint shop are paid alternatives).
3. Same with these old ceiling fans and that neon tube on the floor.
4. There seem to be random barrels and crates in the bathroom.
Again, same with the first screenshot, it does not look like a level, so far it looks like random props that you dragged and dropped into the map. If you approach a level with a certain idea of what it is supposed to look like, and then make sure you acquire or use the correct assets for that, you can avoid this dismal visual quality.
Also, if you want your interiors to look less undefined, you can try lightmapping.