CrysisMcGee said:
Sanitarium. Grim Fandango.Pyschonauts on PC back when it was first released. Diablo 1 and 2...wait
Sacriface. Battlezone.
Yes. FUCK YES. Now you're onto something. At least as far as Sanitarium and Sacrifice (and weren't they both just awesome?).
Battlezone was mainstream, sorry. What you're after is Uprising, the game Battlezone ripped off.
Grim Fandango and Psychonauts are not obscure, they're cult classics. That every second person on this thread brings them up is testament to that. They're like Fallout without the Bethesda sequel to bring them back into the limelight after 10 years.
Whoever said "Worms", shoot them. Shoot them in the face. Even Team 17's older games don't count as obscure: Alien Breed, Body Blows, okay, maybe Phoenix. Nobody knows Phoenix at least. I loved Team 17, I wish they'd make another game that didn't have Worms in the title...
Now, while I'm actually making contributions instead of debunking others:
Warzone 2100 - very much like Earth 2140/50/60 and probably older;
Grizzly - like Mortal Kombat for Mac. With teddy bears;
Transylvania for Mac Plus (I gather it ran on the Mac Classic, too);
Arabian Nights (and no, not the re-named Prince of Persia 3D, the 2D platformer for the Amiga with the awesome music);
Beyond Divinity has already been mentioned - it's the first sequel to Divine Divinity, mentioned earlier in this thread;
Finally, will people please stop mentionning Japanese games like Breath of Fire. I'm sorry, but if it's been anywhere near Japan then there's a group of fans larger than your country (or state, if you're in the US) still updating their walkthroughs. Let it go.
Oh and one extra-final thing, Septerra Core was not only obscure, but awesome. I only know one other person who's played it that didn't discover it through me.