It's Planescape Torment. Incredible story in an utterly fantastic setting unlike anything else out there.
And the characters? Well, we've got...
A floating wise cracking skull voiced by Rob Paulson (of Animaniacs & Pinky & the Brain fame along with a billion other cartoons)
A half-demon thief voiced by 80s pop musician Sheena Easton
A celibate succubus voiced by Jennifer Hale (the One True commander Shepard)
A malfunctioning TV-thing from the plane of order voiced by Homer Simpson's Dan Castellaneta
An animated suit of armor with an obsession for justice voiced by Keith motherfucking David
plus a wandering monk fallen from his people with a blade forged of pure chaos and an eternally self-immolating sorcerous pyromaniac
Each companion carrying its own tragic history and relation with the main character who beautifully tie together with the themes of the game. It's just fantastic.