Well Ibra himself said that Silva is better than Puyol, Thuram Cannavaro and a bunch of players combined.

And he's been saying this for quite a while. I don't always agree with him, but got to hand it to the Swede for the respect. It's not that Silva is just good at defending, it's how he makes it look effortless and unnoticeable.
I am aware anyone reading this text knows this, but next time pay attention to Silva and his off-the-ball movements instead of the play and see what I'm trying to get at.

He's anticipating the game, making clearances, covering for his teammates, marshaling the defense. We'd be lost without him, I am sure.
I still think he can improve further in the next couple of years, as he gains more experience and composure. He'll be scary good then, I reckon. Maybe, just maybe, in the league of Nesta in his very prime.

And that's good enough it gets for most mortals. Sometimes I wonder how lucky do we get!? Clubs like City, Chelsea, Barcelona, Madrid, even United would pay bucket-loads for this guy.