A 4x strategy game that had almost everything. Including bugs and poor performance. Or good AI/diplomacy.
Different types of weapons (plasma, lasers, mass drivers, missiles, rockets, cutting beams) all with different damage profiles, min/max/optimal ranges, power usage and supply cost.
Different defenses to counter different weapons (shields/defectors/PD).
Ability to target different sections of the ships, including individual weapons.
Boarding parties. Deployable fighters, bombers. Carriers that carried battle riders (essentially destroyers), and bigger carriers that carried battleships.
Different class ships (cruisers, dreadnoughts, leviathans), different FTL drive for each race that played differently, different ships design philosophies based on race.
Tech tree that had feasibility (your race might have a predisposition to mass drivers and being able to research them, but the RNG gods might decide that you've failed the feasibility study and be blocked from doing it). Salvage ships to steal other races tech. And a slaver race doing slave raids on your planets, stealing your civilian pop.
WMDs to take out enemy planets (zombie plague
).
Launched in a **** poor state, they kept working on it releasing an expansion and new race for free - essentially as a re-release of the game. Unfortunately there were issues between the devs and paradox, so the game was never really 'finished'. Still played 340 hours on it. Pew Pew! Also got some desktop wallpapers from it