Outstandingly unique, intelligently comedic, and incomparably atmospheric; the masterpiece I'm talking about is Black Isle Studio's Planescape: Torment. Feelings of love, of loss, and of determination and fascination are associated to the mere recollection of the game's name. This is a game which truly influenced my life, the game was released in 1999 and its philosophical themes and thought-provoking dialogue were partially my inspiration, after a life-time of studying pure science, for choosing a typically arts-related subject - Philosophy - as my university degree back in 2001.
The main story-line, the self-discovery of an immortal who only suffers the symptoms of amnesia where a normal man would encounter death, acts as a solid overcoat to the true beauty at the heart of the game - the engrossing artistic tangle of sub-plots, metaphors, expression, and imaginative themes. One such recurring story node is central to this, the brutally profound effect which the protagonist's many lives have had on the individuals who have come and gone in the PS:T universe.
For those who get sucked in PS:T is a game which will cause the thinker to challenge his very perception of the real world, and will shortly after lighten the mood with base-level tongue-in-cheek humour - not dissimilar to the dialogs in Fallout and Fallout 2 with which PS:T shared much of its development team. Much to the credit of lead developer (read: creative coordinator) Chris Avellone, the interweaving of the graphical design, musical score and novel-like finesse of the game produces something that is more emotionally immersive than anything else synthetic I've come across.