No brainer (aside from my main nomination), SMB3. Epic game and the best Mario Bros. game ever (that's not including Super Mario 64, etc, I said Bros.) the best selling game of all time on a single console, 11 million copies, this is the Thriller of the NES gaming system. Smooth control play, a very long lasting playability and it doesn't get tiring even after 15 years of playing!
Sorry that Space Invaders got paired with it, but it is a no brainer unfortunately!