Space combat. I loved X-Wing VS Tie Fighter on PC and put TONS of hours into StarFox 64. These games are great.
Beat-em-up. Even "newer" beat-em-ups like Scott Pilgrim and Castle Crashers intentionally throw back to exact same mechanics that older beat-em-ups used. With today's tech, interesting twists could be put in the genre.
JRPG. Yes, I know that there are JRPGs still around, but nearly all of them suck. I know I'm just being nostalgic here, but I miss the days when names like Chrono Trigger, Final Fantasy III(VI), Secret of Mana, Final Fantasy VII, etc...DEFINED the RPG. Nowadays games like Skyrim define RPG, which I have no issue with, but I miss the days when a game could lay out a fun, deep, and engaging story that, while linear, was just great.