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?
OMG, I can't believe no-one's mentioned BeamNG.drive. The stuff that game simulates is off the charts. It's been in 'early access' forever, but if you're even remotely interested in driving simulators, it's the gold standard for a realistic driving experience. Crashing in VR in this game is the most visceral thing ever. It'll change you.
Here's a clip of me driving a RHD Piccolina around one of my local roads a kindly modder added to the sim until I crash catastrophically.