We got a real kick out of seeing the evolution process of our in-game planets/moons/asteroids across 4 years of work. Went from crap to decent! I'm outlining our approach below in case anyone's interested.
The game is Lilith Odyssey:
2016: We started to create planets for our open-world galaxy thinking "realistic texture" shaders would be the most immersive. But the planets appeared stiff and weirdly blended, as if straight out of Goldeneye. Our UI was non-existent, save for some boxes that we knew would hold player items, health bars, and environmental details.
2017: Matte shaders started to look better with the lighting and shadows created by the environment offered depth. We knew we were heading in the right direction. But the textures still felt dark, a little "dead," and too smooth to be terrain. As for the UI, we pretty much threw everything against the wall -- health bars, atmospheric meters, item slots, resources gathered. etc. -- and it became VERY busy. We knew we had to trim.
2018: Toon shaders baby! They felt right for the vibrant look we wanted, and we could more easily depict (and replicate) illusions of planetary topography. Trees and rocks "popped" more. According to feedback at the time, our planets looked "cute," and to us that meant a style was emerging/coming together. The UI is still dominating screen space with an overload of info. And the colors/boxy look clashes with the looks of the planet.
2019-2010: We kept tweeking our toon shader library so that we had various sets of color spectrums for the ground and water colors of each biome type that would be generated (for example, desert planets would be various shades of yellow/peach, forest planets have various shades of green/blue, etc.). The goal was to program the generation of these planets so that land/sea/background space colors would all complement each other to create ~atmosphere~. We also added weather (snow, rain, meteors, methane hail, etc.) to planets and our dinky low poly animals started coming to life as well! The UI was SHARPLY pared down, leaving only data points that we felt were essential and, importantly, shading it so that meters/info/data blends more seamlessly into the action on the screen.
From there, we felt ready to use our planetary biome data points to generate more than 1000 planets, moons, and asteroids that would populate our in-game galaxy. Each world can be visited and is unique, with its own mix of environment, weather, plants, animals, and civilization.