Perfection like this doesn't come by often.
The gameplay is simple, but amazingly in depth. One finds themselves sitting in front of the TV for hours when it feels only like minutes. Battles are quickly paced and always exciting, never boring, but sometimes frustrating -- and when it's frustrating, you just try harder.
The unlockables really make this game. From musical scores to original courses, you never get tired of seeing windows break and getting prizes. And there's lots of prizes -- chances are, the normal gamer may never unlock all of them.
Most surprising to me was the entertaining gameplay found in the Subspace Emissary -- I thought, that so long as you chose the right characters, the platforming was entertaining, and beating up the Primids never got tiring.
The whole presentation is perfect. The fighting feels perfect. My only problem with the game was my online experience, but that was because my own internet went down -- not Nintendo's.
This is by far the best in the series, and I'll be playing it for years to come.