1)Outcast for me was a amazingly immersive game almost felt like a movie and the music pieces along side it probably helped. There was alot of rewarding content at that time for exploring;p and the environment was diverse.
2) Mechwarrior Commander My Rts dream game of my youth. I was quite fond of how various bits of your Mech would get damaged and almost unusable, i.e if your leg was damaged and you ordered a unit to jump jet it would still be able to but would structurally damage itself on landing
Other such games as Asherons call 2, planet side, C&C Generals almost come high amongst other older game. My memory is taking a walk over the horizon right now and isn't available for work.