It may not have been the most groundbreaking or influential as some of Mario's launch adventures, but on a technical level, I have to give the title to Rogue Squadron II.
I cannot overstate just how mind-blowing that game looked back in 2001. DF are right; on a CRT screen, back in the days where people were used to PS1/N64 or early PS2 graphics, Rogue Squadron II almost looked like movie CGI at first glance. It was packed with effects that even most Wii games lacked; bump-mapping all over the place, volumetric fog, self-shadowing, etc. Individual laser bolts cast dynamic light, the polygon count was obscenely high, textures were crisp and detailed, and for the most part it blazed along at 60fps.
Mario 64 was pretty staggering in its own right in this respect, but the only game that's ever made me double-take as hard as RS2 was the original Gears of War.
