[Ronin4hire]

Genki is excellent for a class/group environment I find. For self study I suppose you could use Genki as the grammar builds on top of each other but as others have pointed out it's limitations in that regard, then perhaps you should search around yourself before you buy.

Anyway it's the prescribed textbook series at my University. The book I'm using next year will be the "Intermediate Japanese" version of Genki made by the same people.