I forget, which book was that? "For Dummies"? (Probably not, doesn't sound like it.)

Anyway, you sound unhappy with it, which is a shame. On the other hand, I'd probably love it. My attention span is really short, and I usually grow to loathe long, extensive explanations. But especially when they're accompanied with a bunch of repetitive exercises. Like in the book series "Practice Makes Perfect". Now, if you think you could use 20 more exercises with "einem"/"einen", pick that one up. Or they might have a whole book dedicated just to that. (I know there's one just for Spanish verbs.)