80. Ultima Underworld: The Stygian Abyss (Blue Sky Productions, 1992)
A game that was built from the ground up to not just be a more realistic kind of puzzle-driven dungeon crawler, but a full blown life simulation too. To that end, you had skills not just oriented around combat and spellcasting, but for swimming, conversing, identifying items and bartering with NPCs among many others. It had a lighting system and rudimentary physics for platforming, letting objects bounce off of walls (and activate switches) and no single set solution for most puzzles, letting the player take an innovative approach to figuring out the game's mysteries. Downright mind-blowing stuff for 1992, and the influence it's had on the industry since is immeasurable. inspiring games like Elder Scrolls, Half-Life 2, Deus Ex, and numerous others. It's a bit clumsy and awkwardly slow to play today, but it's nevertheless a great game and an important building block for gaming as a whole.
79. Astro Boy: Omega Factor (Treasure/Hitmaker, 2004)
Not only my favorite Game Boy Advance game of all time, but one of the finest from the Sega, Hitmaker and Treasure camps to boot, Astro Boy is a great experience all around. Combining numerous Osamu Tezuka characters into one enormous storyline, as well as several different gameplay styles (beat-em-up and scrolling shooter being the most prominent), Astro Boy is also a very challenging game. But the real genius of it all is in its implementation - by finding characters, Astro Boy's "Omega Factor" develops, unlocking new abilities and upgrades. A pretty clever way to explore the universe of Osamu Tezuka (which you really should anyway; the guy is a legend).
78. Tyrian 2000 (Eclipse Software, 2000)
75. Marvel VS Capcom: Clash of Heroes (Capcom, 1998)
73. Castlevania: Symphony of the Night (Konami, 1997)
72. Donkey Kong Country 2: Diddy's Kong Quest (Rare, 1995)
Another example of a groundbreaking game getting an equally groundbreaking sequel, Donkey Kong Country 2 had more of everything to offer. Stage variety, hidden secrets, animal companions, sharper visuals, better music... it really was a step above the first DKC in every respect. Hell, it even took a page from Super Mario World's book and had entire hidden worlds to discover if you found enough special coins to unlock them, and these stages were among the toughest the game, so your skills had to be honed to a T just to stand a chance at making it through them. There were even some clever cameos from other Nintendo characters if you managed to collect enough hidden DK coins before the ending. Now if only they could get their act together and make another sequel even half as good as this...