Classics

[Tallim]

Lords Of Midnight
Midwinter
Jet Set Willy
Shadowfire Mission
Wasteland
Ultima 7
Day Of The Tentacle

and many many more that in a most hipsterish way I doubt a lot of people have heard of on here except for the older posters.

 

[thesilentman]

Super Mario Brothers 3- The embodiment of "difficult, but awesome."

Demons'/Dark Souls- Yet another "difficult, but awesome" deal, and does it with such good execution as well.

Shadow of the Colossus- DEFINED boss battles. Didn't just create them, the game defined them to the point that this is what a boss battle should be

Journey and Flower- Art. Just pure, euphoric art. You all need to play these games if you haven't already.

Those are all that I'm thinking right now. I'll come back if I have more.

 

[Bad Jim]

MineCraft - ideally with Tekkit mod
Starcraft
Total Annihilation
Doom
Unreal Tournament
GTA San Andreas and Vice City
Deus Ex
Hostile Waters
Elite 2: Frontier or First Encounters
Elite
Freelancer
Portal 1 & 2
Braid
Sokoban
Lemmings
Boulder Dash
Puzzle Bobble / Bust a Move
Floor 13
Ecco the Dolphin
Desert Strike
Sonic 1,2,3 & Knuckles
Super Mario Bros
James Pond 2
Rainbow Islands
Turrican 1 & 2
Head over Heels
R Type
Uridium
Exile (there are several games called Exile, I'm referring to the game by Audiogenic, originally for the BBC. The Amiga had the best version)
Populous 2
Cannon Fodder
Another World
Spy Vs Spy
Dyna Blaster/Bomberman
UFO: Enemy Unknown aka XCOM: UFO Defense
Walker
Putty Squad
Monkey Island 1,2 and 3
Day of the Tentacle