Quoted By:
You mean games that you actually have to be smart to play, or just semi-complex systems? Or is it just puzzle games you're looking for?
Complicated games would be like Magic: The gathering (building your own deck and shit), Football Manager, most Paradox games, Dwarf Fortress, Path of Exile...
A bit easier on the systems I guess Rimworld, Factorio, Project Zomboid, Anno series...
Puzzle games I'm not too into, but Portal, blue prince, Silent hill and the like could pass
Add some more context and I'll try to help narrow it down better