swarm simulator 2000
you are the latest alien menace of decent amount of choices of "what type of menace" (at least "offensive", "infestation", and "sneaky") affecting playstyle and units
the universe is a 4x game in and of itself and you have to rely on that to make progress- you aren't even a planet to start with
countries will be managing their diplomacy, expanding, trading, and warring all of their own volition (having seen 4x AI before this is way easier than it sounds), distant worlds style ideally, but the universe doesn't need to be randomly generated- just the inhabitants
ships are simulated in the "fleet" sense, doesn't have to be detailed, but your interactions should affect the wars or economy- shit on an integral war supply fleet and boom, the front crumbles, or similar. small countries should seek overlords or unions to fight large countries off, the universe should make "sense"
the goal is to eliminate all other sentient life and to do this, you'll have to grow and grow. it should be exceptionally difficult to just assault existing empires and zombie the fuck out of the universe
there should be 3 layers
the 4x you aren't quite playing, you are fighting anyone and everyone even if they want to use you to their advantage, don't know you're there, or are crumbling under your neural parasites
this should be almost Pandemic style for the player, evolving, deploying your forces to do things, growing, and seeing who and what is where, and not much else, you are a bystander and also the big bad guy- much like Pandemic, as you grow, space nations will try to band together to eliminate infested areas, keep their countries in lock down, and so forth
there should be some events to keep it spicy, but you're the galaxy killer- nothing else of that scale
"sneaky" menaces get to declare wars and do some basic empire-fucking things like genocide and creating illegal weaponry if they've infiltrated administrations
not too complicated, but if you're either an infestation or offensive menace, your fleets will need at least some combat interaction
I would envision something simplistic like the Star Wars Empires at War's space combat, move about ships, maybe target parts of enemy ships, maybe use special weapons/abilities, and that's it- all presets, though, customization would be a timesink
for offensive and infestation menaces, you would want a sort of top-down stealth or combat sim, I'm thinking a tactical rpg, something XCom style perhaps, with actual AI
if they don't know you're coming, they should be doing very basic crew member/civilian shit, food for your xenos or targets for infestation- more units to snag stealthily, if you haven't really been identified but you're spotted things start to ramp up
if they know you're coming, armies or guards would be at the ready, maybe heavy duty weaponry even
if you're world-destroying menace tier then they go all out, civies in shelters and lasers fucking everywhere, better hope you're stealthy enough to get behind them or have some biological tank-tier units by this point
hand-made "maps" that stay the same, just like the universe- no need to be super unique, but at least decent variants
enemies should be based on race, tech, and status- just shit on someone's reinforcement caravan and made them lose a war? their resource stats should be low, less tanks and ships. fighting a turbo-empire with your shitty band of bioweapons? expect to lose, neverending reinforcements, and if that doesn't work, expect exterminatus
if you can deliver well on at least a few of these aspects and them out, this sort of game would be loads of fun, even if maybe the 4X bit isn't stellar, or instead the combat isn't stellar