Beyond Exceptional
In my mind, Ristar should have been Sega's flagship series. The game mechanics of Ristar are so much more pleasing and precise than those of Sonic the Hedgehog's: the arm-stretching in particular works spectacularly well.
The game design is amazing- Each world features 2 levels followed by a boss. Each of the levels in any given world are completely different from one another, featuring distinct colours, designs, music and enemies.
The soundtrack is also excellent. Every track in the game is vibrant and unique. The music in some stages (planet sonata 1 in particular) will always haunt me.
Ristar has some unbelievably solid parts and still manages to be more than the sum of them.
If one game has ever deserved to be called "underrated", this is it.