Yaya can tackle, he can pick a pass, he is decent in the air, he works hard (mostly) and he gets some important goals. But his real advantage are those lung-busting runs he does. He is IMO one of a number of reasons why we are at the moment the best side in England. And he will become more important.
We are seeing increasingly teams play us with a very defensive attitude - the whole '2 banks of four/10 men behind the ball' thing. When you are facing massed defences like that, which we will, you can pass around them, which is possible but very hard, you can down the sides and behind them which is also hard and the area is packed when you do, or you can run at them. Running at them takes players out of position, leaves space elsewhere, causes panic and often results in a free kick if nothing more. So Yaya gives us a way of breaking down stubborn defences which - as Everton showed - we are going to need more and more.
Silva's passing is at present the best in the prem, we have wingers & full backs who can attck and cross, and we have a number of players like AJ who are comfortable running at defences. But make no mistake, perhaps because of his size and his speed and his power, when it comes to running at a defence Yaya is just magnificent.
We will miss him in January, let's hope for a decent draw in the FA cup (and, fingers crossed, the Carling Cup semi final ;-))