A couple of years ago I would have said Marvel vs. Capcom 3. Obviously that's actually happening now so I have to think of a different answer. I would have said Sparkster too but THAT got a sequel that was decent but too damn short. Really, I just seem to be on a lucky streak with sequels and retro revivals.
Let's see....
I guess I would say I really wanted a third Chrono game to succeed Chrono Cross. There were rumors for a long time, but it's reached a point where we all have to admit it's probably never going to happen. Cross wasn't a terrible game, but it had too many characters, the battle system wasn't as exciting as it was in Trigger, and the story was a rather cruel middle finger right in the faces of the cast of the first game. I was hoping for a third game to come along and retcon all that, but it doesn't look like it was meant to be. I think the old battle system in Trigger is still pretty fun and impressive even by today's standards, although I'm sure a next-gen version would have to add a few bells and whistles to it. Maybe have different commands for attacks like Mario RPG did so each character feels different.