If I'm allowed to go back in time, Super Mario Bros. 3. It was (and is) gaming perfection. There is not a single real flaw the game has that I can think of, and for it's time it was massive and utterly stuffed with content.
Outside of that? Maybe Final Fantasy IV. To me, that is still the apex of great "jrpg" style gaming. Again, I can't really think of a single flaw the game had, epic soundtrack, great story, great characters, great system (only FF game to have five person parties), great pixel graphics that still hold up today despite their age. Again, for it's time, a fairly enormous game. And while I love other later Square games, I still think they outdid themselves with their first SNES entry.
I could honestly say the same thing for Street Fighter II as well. To this day, I don't think I've ever played a more complete fighting game, that got any closer to "perfect" than that. Not even Super SFII, I'm talking just the original game, or perhaps Championship Edition because of the playable bosses.
Any MODERN games I'd give that kind of nod to? I was rather partial to Twilight Princess, though I'd really have to think about giving it a 10/10. I think, between the two, Mario Galaxy 1 deserved a perfect score over 2, and I thought it was kind of absurd that outlets like IGN gave 2 the perfect score. I didn't find it to be a "better" game on any level. Yoshi or not, the game, while not BAD, simply felt like another Lost Levels to me, and I thought all around the level design and power ups of the first game were just better, it was better total package to me.