According to a poster on the BBS:
'When he took over as team manager at Leverkusen he was working alongside someone else who was responsible for coaching. It was during this period that Leverkusen did quite well. As soon as Hyppia took sole control it all went to shit pretty quickly'
(That coach being Sascha Lewandowski, who is now Leverkusen's manager)
Win ratio while working with Lewandowski was 54%; win ratio when working alone was 51%, including the dreadful run at the end which led to his dismissal.
Personally, I'm in the "quite excited, but aware it's a risk" camp, but it's simply not true to say, as the poster on BBS does, that he didn't have success without Lewandowski. Just by way of comparison, Oscar's win ratio in the league was 41%.