Panel de Pon = Tetris Attack. Lolicon fairies become the Yoshi's Island crew along with the completely arbitrary addition of the lucrative Tetris name. A pretty rational change, all things considered.
Trying to keep it to major changes since mentioning slight visual edits would make the list 10,000 entries long. Things like Vampire Killer to Castlevania: Bloodlines where Eric Lecarde was de-bishojoized are probably too minor to mention.