Franchises

Here is every game I've looked at that is part of a long-running series.

Castlevania

Castlevania 1
Castlevania 3: Dracula's Curse
Super Castlevania 4
Castlevania: Bloodlines

Final Fantasy

Final Fantasy 7
Final Fantasy 12

Gradius

Gradius 1 (Arcade)

Gradius 2 (PC Engine CD)

Gradius 3 (SNES)

Nemesis (Game Boy)

Gradius: Interstellar Assault (Game Boy)

Salamander (Arcade)

Life Force (NES)

Gradius Gaiden

Gradius V

Megaman

Megaman 1
Megaman 2
Megaman 3
Megaman 4
Megaman 5
Megaman 6
Megaman 7

Megaman on Game Boy

Mega Man: Dr. Wily's Revenge

Mega Man II

Mega Man III