Welcome to "Doc teaches Old School and New School games"
A few things to help put my list into perspective:
I'm 38...I've been playing video games for about 30 years. The systems I have owned are: NES, Sega Genesis, Turbo Grafx-16, PS1, PS2, PS3, Wii, PS4, as well as PC. That's a lot of games. Also, being a child of the 80s and early 90s, arcade machines were paid a lot of quarters. All but one of those systems will have at least one game, and one game from a system I didn't own will make the list. I like hard games. Check that, I have always liked brutally hard games. Back in the day, we didn't have the internet to help us figure things out. Games that challenged were always welcome. For this list, one game per franchise, otherwise 20% would be one franchise, and a few other might have had multiple entries. Most of the time, the chosen game will be my favorite from the series, but I think in at least one case a different game is chosen.
I made my list by going through lists of every game published for the systems I owned except PC (that list might not exist or would be too hard). My initial list had 50 nominees, so I'll start with 25 honorable mentions:
NES
Super Mario Bros. 3
Faxanadu
Bionic Commando
Blaster Master
Castlevania
Dragon Warrior
Mike Tyson's Punchout
Contra
Strider
Shadowgate
Sega Genesis
NHL 95
Road Rash III
Shining Force 2
Shining In The Darkness
Sonic The Hedgehog 2
Sword of Vermillion
Arcade
NBA Jam
The King of Dragons
PS1
Final Fantasy 7
Syphon Filter
PS3
Dragon Age: Origins
Heavy Rain (#26)
PC
Baldur's Gate
Ultima 3: Exodus
Wizardry 8 (#27)
Coming tomorrow: The newest game on the list, and the oldest game on the list