I'm gonna have to give into nostalgia and say Jedi Knight II: Jedi Outcast. The amount of time I spent on it as a kid was pretty astounding, and even today it's fun to go back and play through it every now and then.
I've been playing a lot of Red Dead Redemption 2, so I'd love to see some panoramic views on a shiny new monitor. Not everything I play is so demanding, though - I'd also be spending plenty of time peering down at my parks in some Open Rollercoaster Tycoon 2. ;)