Mega Man 3

Mega Man's third game takes him to... hell, there's no setting or story to these games. You had to fight Hard Man, Snake Man, Needle Man... and 5 other robot masters. This game introduced sliding and Rush to the series, but Mega Man 3 was best known for the Doc Robot stages, which forced you to revisit modified versions of past stages and fight bosses that would impersonate the robot masters from Mega Man 2. Because of these boss fights, Mega Man 3 had the most boss fights of any Mega Man game in the original series at a total of 29.

Mega Man 3's password system was so easy to crack that Nintendo Power actually made a complete guide to setting up your password however you wanted without even taking up a full page. Not that it was necessary if you were stuck; there was a debug code left in the game that allowed Mega Man to jump really high, jump out of pits, and achieve near-invincibility in almost every level.