Teutoberger Wald was a tragic defeat for the Romans, but I disagree that it was the decisive defeat conventional wisdom has it. There were several later punitive campaigns where the Romans marched at will across Germany. Germanicus decisively defeated Arminius at great cost to the Germans. I think the Romans just decided the Rhine was the best natural barrier for the frontier and Germany just didn't have the riches to justify the expense of occupation. Besides, with Arminius defeated they were able to establish client states across the Rhine.