As a developer, I'd never thought I'd like to solve for getting off the planet, fighting monsters, building trains and tracks while trying not to pollute too much.
If you find pollution is not a challenge, try a deathworld run. If you can already beat a normal deathworld - turn down trees/moisture, turn up pollution diffusion ratio; then you can add rampant, armored biters, bob's enemies, etc. I recommend the infinite ore patches mod as well, you will be defending the starter patch for a veeery long time.
My favourite recent challenge was "New Game +", you start with all tech (perhaps except damage upgrades) unlocked, but biters also start at 1.0 evolution. You technically don't need any science to launch a rocket, but you still have to figure out how to build a mall (and enough defences) before triggering a single attack.
It really is, isn't it. You're incentivized to protect every last thing, not because of some arbitrary points system, but because they're all part of a big, interconnected system that needs to work in order to survive.
In my book, Factorio is up there at the top of best games of all time.