Simulators are one of the earliest PC game genres, and remain compelling experiences to this day, even if they're not as popular as they used to be.
I like all kinds of combat flight sims; the MS Combat Flight Simulator from 1998 was something special, and I've had some similar fun in IL-2 Sturmovik. The newest civil air sims are pretty great too, I'll pop on a podcast and make a flight. They're particularly cool in VR.
I've also found the MechWarrior games to be fun, but I've only played 2 and 5. I got to play a bit of Steel Battalion with the full crazy controller at a con a few years back, and that's got to be a lot of fun once you really know what you're doing.
So what's your favorite sim?
I spent a lot of hours in F-19 Stealth Fighter on the Atari ST as a kid. The manual for that thing was unbelievably in-depth. I'm utterly convinced I could fly real combat missions in that (fictional) plane.
YES! I PLAYED THE SHIT OUT OF THAT GAME!!!