When mentioning the retro game era, we commonly think of Mario or Zelda first, forgetting other classics that were out at the time. MegaMan, first released in 1987 and became Capcom's most prolific series, with the publisher still releasing these games today.
The story starts with you, the player, as a modified housekeeping robot sent to defeat the Mad Scientist Dr. Wily who is attempting to take over the world by reprogramming six powerful robots. It is your job to defeat the bad robots and find the evil Dr. Wily to bring him to justice. The unique selling point for this game was that it was the first game to employ a fully weapons based combat system, a lot different from jumping on the heads or hitting enemies with a sword. However it was the way you could play the game that set itself apart from the rest. MegaMan was the first game where you cloud play the chapters in any order you see fit (which was a lot different from the linear progression of Mario and Zelda). The reasoning was that each boss was more susceptible to a different type of weapon and after defeating a boss you absorb their special ability, helping you to defeat the other bosses who is weakest agents that weapon.
MegaMan was renowned for being fantastically difficult and still provides a challenge for today's audiences. We ultimately gave this game 6 out of 10, but this is due to how the game would fair in the current day and not when it was originally released.