As a pile of code and mechanics, it's not that special. But as a channel by which friends can come together, it's a perfect storm of chaos.
What really makes it work is the fact that it forces driving controls into your boat. At first, it's a little frustrating, but after a few games, you get it. Not in that you're good at using it, but in that you understand that all control is tied to an inherent risk and reward: the faster you go, the less control you have over your ship. This lends itself amazingly well to couchplay and leads to hours of rambunctious play.
Also the characters are all cute I would like plushies of them.