MTZehvor on 02 May 2013
I think a bit of it comes from the fact that SMB, Zelda, and Metroid were released in such quick succession from 1986 to 1987. Not only are the three so closely together, but they essentially compromise the entire spectrum of Nintendo gameplay. Mario is the carefree, linear, cartoonish, appeal to everyone end of the spectrum, while Metroid is dark and nonlinear with a focus on exploration and figuring things out yourself that doesn't appeal to as many. Zelda's probably the middle of those two extremes.
Saleswise, sure, it's nowhere near as impressive. But in terms of gameplay inventiveness, it's one of the three defining parts of Nintendo's history.
