What I think is "mediocre" is the Gamespot review on this game.
Much is said about the game's lenght, but to that I'd say there's alot of full retail games out there who pale in comparison and are just about some more minutes longer. It's amazing how much they managed to pack in a 40 MB download. And besides, if you devote some more time exploring hidden corners and experiment more with the 3D elements in the game, you'll be ending up playing a lot more than the 3-hour timespan so argued about.
In my opinion, this game sets a welcome standard on what Wiiware games should be for the 10 dollar pricetag.