Let's be honest, Zaheer Khan, Sreesanth and VRV Singh aren't really "top class bowling" and he hasn't had to face Anil Kumble that much in the test series. He does have a very big technical flaw and drifts around his stumps and will work the ball to the leg side more than is necessary. Comparatively he is quite weak through the off side and I haven't seen him time many good shots through cover or mid off that have reached the boundary.
The point has been raised about his age and having already played 50 matches, off which he has captained an amazing 42. That is ridiculous, he started captaining South Africa when he was 21 with guys like Gary Kirsten, Mark Boucher, Shaun Pollock, Jacques Kallis and Herschelle Gibbs all still in the team. Imagine being in that scenario, coming in to a test team, having a very good average of 55 after only 8 games and then being asked to captain a side which includes all this veterans and legendary South African players. No wonder the poor guy was going to have a slump in his batting, it's been 12 matches since he has scored a century in test cricket.
Talk all you like about his technical flaws, but when you think about it he has done amazingly well in his career so far. After 50 matches he has 3 double centuries and 11 centuries, almost 4000 runs at an average of 47. If that's not sucess, then I don't know what is.