When it comes to metroid, the game to play is Super Metroid. I found Metroid 1 to be good, but it has not aged very well, super metroid on the other hand still remains one of the all time greatest 2d games. Other classic NES games of some importance worth checking out are:
Probotector (Contra)
Batman
Shadowgate
Blaster Master
Bubble bobble
Mega man
Mr. Gimmick (for its amazing sound chip)
Journey to Silius (yes I do love Sunsoft games… amazing sound)
Kid Icarus
Gradius