[WIP][C+C] NES Style Side-Scroller Tilemap (and more!)

[heyguy]

Hello all! I made this NES style side-scroller tilemap a while back and I'd like some feedback if possible. My intentions were to get better at pixel art by creating something with a limited palette and to possibly use the tilemap in a game. I completed this to a "finished" state but I think it could be improved. What does everyone think? Overall, I do like how the piece turned out. I really like the sand but that's because I straight up copied the look from Ninja Gaiden 2! I'm sticking with a NES color palette restriction and I'm trying to use color in interesting and detailed ways. I'm sort of unclear on all NES restrictions though. Can I also use any four colors on one sprite? Anyway, so there's a thread on this site (or pixeljoint) about the game Shatterhand on the NES and its awesome art. I'm sort of trying to recreate that style of artwork.

I've begun prototyping and I find I'm still lacking enough tiles to create a large, seamless, visually cohesive level. That's why I posted this here. I'd like some feedback on it's current form because I'm going to start expanding on it. My setting is Metroidvania-type game on a rocky desert planet with a science station on it. This scene is a small science camp out in the desert leading into a cave installation on the side of a mountain. I need tiling walls and ceilings! Anyway, thanks for looking! Third image is just art of the tiling background.

[MysteryMeat]

I'd say more variation. Cheat a little for the benefit of overall look.
For example,  on the background with the watertank (?) against the wall, throw a crack in here and there and maybe some brick/plating lines here and there to give it more texture. that kinda thing. If you're feeling like giving it a more opressive atmosphere, some smoke in the distance now and then could give it a more storied look.
Minor alterations in the tileset like that can do a lot for keeping it all visually interesting.