The one Game.

Unreal Tournament 1999! Still a classic, still holds up today and is crazy, bloody fun. I'd say 2004 is actually better for everyone, but it's the nostalgic factor which keeps me playing my disk version of 1999 to this date

Deus Ex Game of the Year is another contender, one of the most phenomenal games of all time and plays out like a novel. It's absolutely brilliant, and I have nothing but praise for it. The only thing outdated about it is the graphics - which is unsurprising considering it was released around 2000. The only reason I pick Unreal over Deus Ex is the nostalgia factor since Unreal was my first video game as well, ever.

Mountain

Tales games, Or Tales of Abyss to be exact, my favorite old game