I've been recently been thinking about Arkane Studio's Prey which is a immersive sim, with a pretty good rogue like dlc, that probably has one of the strongest hooks of any game I've played. If you liked Halflife, System Shock, or Deus Ex it's definitely worth a play.
Are there any titles that might not have been commercially successful that you feel everyone should give a shot?
My favorite thing about Illusion of Gaia has to be the fact that the manual contained a complete walkthrough of the game, at least in the North American release. Unless it was the same energy as "the dumb Americans ~(who invented the genre and introduced it to the East)~ don't understand RPGs, so we'll make Mystic Quest really simple and dumbed down for them" I don't know why they did that.
Also, I was like 13 when I got my used copy of Soul Blazer…is there a more melancholy game on the SNES?