The rarest officially released NES game is Little Samson, a sidescroller action shooter released in 1992. 

Why is it so rare? There are a few reasons for why it's so sought after. It was released while the Super Nintendo was already in production and many people had already moved on from the NES. Few copies of the game were made at the end of the NES' life, nor was it then produced for the SNES. It was also made by Taito games, who's characters aren't as recognizable compared to the Nintendo Icons of the time. Had Taito been a highly regarded powerhouse of gaming at the time, more copies would have been made and bought.

Because it was a late release NES game, the development and gameplay of Little Samson are top notch. Regularly compared to Mega Man, the game's design from the player movement and scenery, to the overall storytelling in the game places it in the upper echelon of NES titles. 

Check out some gameplay of Little Samson!

Here's a link to Little Samson on our site in case you want to check it out:

https://www.dkoldies.com/little-samson-nes-game/