Cities: Skylines but ecosystem repair. Plant forests, regrade areas of mountains to mitigate landslide potential, reintroduce species and study their functional relationships with each other... Game progression comes in the form of additional research grants or new area assignments which present new challenges and unlock a new set of tools/procedures, but the successes from previous sites allow for migration of the reintroduced species into the new site.
I've only watched gameplay of Terra Nil, but it seems like it's just an environmentalism themed puzzle game. You could replace all the titles with colors, and all the buildings and what they do with arbitrary rules, and it seems like it wouldn't look anything like an ecosystem sim. It would be like taking the game Lights Out, changing dark spots to "growth", light spots to "wastelands" and saying the goal is to balance out the ecosystem.
I didn't see the late game though, so maybe I didn't see where it shines.
I was hoping this was the direction Dyson Sphere Program would go. I think it would be an interesting twist on the factory management genre if nature was working against you; not in a Factorio "aliens will attack you if they see your pollution" way, but a "you're producing pollution, this is creating more in-climate weather that is damaging your factories and changing the landscape dynamically" sort of way. I think this was the natural next step given that the game is already about climbing the Kardashev scale, producing more energy so that you can construct the means to produce exponentially more energy. Seemed like the natural next step would be exploring the balancing act that has to happen to achieve that energy production without also creating systemic issues for yourself that make it infeasible.
Instead their latest patch adds aliens that attack you 😕.