I was just about to post this. I LOVED Galerians. Had such a fuck-awesome story. Galerians: ASH on PS2 was just as cool. Gameplay in both are kind of whatevs, but holy shit were these games bad ass.
I think most people have cover a lot of the hidden gems here. But I'll throw this one in:
This game is basically Demon's Souls, before Demon's Souls. King's Field definitely had a huge influence on Demon's Souls, but I always thought DS played and felt more like Shadow Tower. ST was a dark, atmospheric, music-less dungeon crawler. It was incredibly difficult too. Weapons and armor breaking constantly, using HP to repair items, etc. It's sequel, Shadow Tower Abyss was superior in every way, but the original is still cool as shit on it's own.
A little trivia for the From Software devote. The actual 'Shadow Tower' became a secret dungeon in From Software's PS2 launch title, Evergrace. Many people disregarded Evergrace as a trashy launch PS2 title, but for someone who practically grew up with From Software, seeing references like this in Evergrace made me appreciate their games even more so.
From Software really knows how to treat their fan base and they have been sticking to their guns since their modest beginnings. It's amazing they are still making games like Dark Souls in a generation where most have forgotten their ways.