I've tried lots of German text books, and 99% of them are essentially very easy grammar tests, which you quickly learn to fill, without actually learning to speak. In Goethe Institut's courses you also simply fill many tests, but in a group. This may help preparing for an exam, but not to learn anything.
That said, I'd love to see excercises on a really hard matter: verb controlling the noun. E.g. ich vermeide <which prep?> <noun|infinitive>. And not just random verb + random object, but sequences of the same verb, to get it remembered.