If you want to know about Sissoko - all you do is watch this game. Defensively incredible, extreme work rate, but not a good passer of the ball.
But, notice the difference in how the team functions with Sissoko as the defensive midfielder compared to when Melo is there. Melo does nothing defensively except alibi running and celebrating when clearing the ball to a corner. If it isn't clear to Ferrara by now how to set up the midfield... well, he's out anyway.
Forza Momo though, you gotta love this guy.