Worlds that make sense
Temperatures and ice follow distance from the star, habitability depends on who's asking, and cities spread across worlds as their people grow, each people building its own way.
I made the star systems more realistic in three ways: what a world is like, who can live there, and how it looks from space.
Realistic worlds
Temperature follows distance now. Worlds far from their star are colder and carry the ices you’d find on cold worlds, unless thick air holds the heat in.
Habitability depends on the species. The same world can be a paradise for one people and deadly for another, because its temperature, air and hazards are judged against each species’ own home climate and traits. A world’s profile shows this for any species you pick. Every empire now starts on a world its people can fully live on; before, some started on worlds their own species could barely survive.
A world’s deposits stay hidden until you survey it, and show step by step as your surveys and probes reach it. The Sun and the 142 real neighbouring systems now come from a data file, and so do the looks of each kind of atmosphere, so they can be changed without touching the code.
Cities from space
Worlds with people now show their cities: streets and districts lit on the night side, spreading as a colony grows and getting sharper the closer you look. Not every people builds the same way. Some live underground and show only faint points of light, some live under the sea with a soft glow beneath the water, others in treetops or along the shore. A world shared by two peoples shows both.
Looks
Mountains now show from every angle. Ridges and hollows stay visible under a high sun, where they used to go flat at noon. Aurorae are rarer: they need a strong magnetic field and sit round the poles, where before they turned up on more than half of all planets. Comet tails have volume and soft edges instead of a flat, bright streak. Systems are wider, so a gas giant no longer seems to sit on top of its neighbours and moons keep a sensible distance. And asteroid belts stay clear of planets.
Battles in a system
Fleet battles now play out in the star system itself, with ships in two formations beside the world being fought over, firing on their real timing, and beams, torpedoes and flashes where the shots land.