Hierro is a key player, but to be honest I feel ne needs to be on top physically, otherwise he's rubbish. The last games he played were awfull.
What I believe has changed a lot in recent games is the fact that since Guti got injured, Helguera has played, and as he is more defensive, we have been way better (when the players were motivated and not tires

)
I have a lot of hopes on Helguera, I really think he can become one top player.
Talking about Campo, I just have one thing to say, sell him as soon as you can Mr Sanz. Karanka is doing a great job lately.