System Shock 2 (1998, I think...).
Look past the flaws (As many as there were), and you have a Ground-Breaking Monster of a game that will laugh at you and Stick Glass up your gums if you even messed one little thing up, and WE like it like that!
And I can remember me pissing (With Exitement.. Of-Course...) myself because I had got the game on Chrismas 10 years ago.
If I could choose a Second and Third, 2nd Would be Morrowind: Back when the series wasn't stagnating so hard you could actually play it without barfing. And Amnesia: While the gameplay and Characters were nothing new, I loved it for it's Immersion and Timeless Plot. While the plot wasn't that good either, I like it because of how it un-ravveled. Instead of being told (i,e Monolouge, Text, or GooblyGook) you actually had to do terrifieing things JUST TO REALISE WHY YOU'RE DOING TERRIFIEFING THINGS.