1. Star Wars: Knights of the Old RepublicStar Wars: Knights of the Old Republichttps://giantbomb.com/wiki/Games/Star_Wars_Knights_of_the_Old_RepublicOpens wiki page
RPG combat isn't really my thing, but everything else (atmosphere, characters, story, etc) is perfect.
2. Riven: The Sequel to MystRiven: The Sequel to Mysthttps://giantbomb.com/wiki/Games/Riven_The_Sequel_to_MystOpens wiki page
One of the most immersive games I've played due to an extremely simple interface, and a detailed world to explore. The puzzles are really fun. There isn't much replay value, but it's so memorable and inspiring that it doesn't matter much.
3. The Last ExpressThe Last Expresshttps://giantbomb.com/wiki/Games/The_Last_ExpressOpens wiki page
4. Deus ExDeus Exhttps://giantbomb.com/wiki/Games/Deus_ExOpens wiki page
I've probably spent more time on this game than any other game I've played. I just wish the stealth gameplay was a little more difficult.
5. Grim FandangoGrim Fandangohttps://giantbomb.com/wiki/Games/Grim_FandangoOpens wiki page
I haven't actually played this from beginning to end, but I can say it's AWESOME.
6. Tom Clancy's Splinter CellTom Clancy's Splinter Cellhttps://giantbomb.com/wiki/Games/Tom_Clancys_Splinter_CellOpens wiki page