Well, the game is really selling on the name power. Even if people didn't know that the creator of Final Fantasy made this game with music from the Final Fantasy Music Guy, the mere fact that it has Akira Toriyama's distinct art style is probably the driving force behind the game's sales. Dragonball is still hugely popular in Japan (there've been over 20 Dragonball games in Japan in the last 4 years alone, apparrently), and Dragon Quest is the most popular RPG series, if not the most popular game franchise over there.

Still, the other names together with Toriyama are pretty powerful. The last time Sakaguchi, Uematsu and Toriyama came together, we got Chrono Trigger.

Famitsu gave the game a very good score (37/40: 9/9/9/10), Microsoft has been marketing the hell out of it, and from the 15 minutes I spent with it it actually feels really good to play. This is Japan's killer app.