Dwarf Fortress and Factorio are what I play. And while DF may be a graphically simple game, it's well known that many fortresses which don't succumb to fun succumb instead to FPS death, as the in-depth simulation eventually surpasses every computer as the fortress grows and sieges build up. It's certainly a demanding game, and towards the late game even on my perfectly working mid-tier PC it slows to a complete crawl. Factorio is easy to run, it's just that I mostly play things like Team Fortress 2, Factorio, Geometry Dash and Dwarf Fortress. I needed some examples and Factorio isn't from 2007, so I picked that. The most demanding one is of course DF.