Puyo Puyo 20th Anniversary. They took the best competitive puzzle game ever made and added a ton of goodies to make it the best package deal. 20 variant game modes, 24 character stories, a comprehensive set of tutorials, a devilish set of chain challenges, and a final challenge where you play against max level CPU while it's allowed to cheat.
It's a tragedy this game was never released in the west, and I can rant for hours about Sega has criminally neglected the series with the half-assed slop they put out now because they know that crossovers will sell better than the main series ever will.