By "obscure" I understad that it's a game that mostly went under radar, that few people has played / heard of.
Based upon this, I have some (i'll will try avoiding doujin games).
Rizing Zan: The Samurai Gunman (PSX) - I'd call this game "the Red Steel precursor, in 3rd person", bacause that's what it is: an 3rd person action game where you play as a Gunman who weld not only guns (duh), but also swords.
Maken X (DC) - A FPS that uses basically mellee attacks, and have a nice "brainjack" feature.
Sanitarium (PC) - As already mentioned, a nice (and disturbing) point-and-click adventure game with a awsome atmosphere.
Bad Mojo (PC) - A cockroach simulator! Well, sorta. It's and adventure game where you play as a cockroach. It's a well known game amongst old gamers.
City Connection (NES, MSX) - You control a car in a mission to "paint" the streets.
Gonzales (MSX) - A platform game where you play as a mexican guy jumping around cactus and stuff.
Pulseman (GEN) - An action-platform game that was not well known back on it's day because it was a japan-only game.
I.Q. Intelligent Qube (PSX) - A puzzle-platformer-wtf game, where you need to match rolling cubes to avoid bein squashed.
There are some others, but these are the first that comes in mind.
choconado said:
(...)
Next, I'll point out a PS2 game. "Rez". (...)
Hmm, well, technically, REZ is a Dreamcast game ported to PS2, not a PS2 game.