Too many great comments on here, so I'm just gonna chime in and say...Resident Evil. I've wanted to play one of the games in the series for a while, but never got around to it. From what I've heard, it started off by reinventing the horror game genre, and then went on to becoming a bizarre shoot-em-up. I heard the HD edition of RE1 is coming out soon; I might have to jump on that boat.
I have never played Super Metroid. I am in the correct demographic to have played this and I have played the majority of the quality titles for the SNES. I simply have never played that one. My peers that played games back in the day all recommend it and I did play the first on the NES. I even played a little of one of the GBA Metroid games.
A part of thinks that I should go back and play it, but then when I do get time to play games at all I enjoy the comfortable hoodie that is Skyrim.