Mascherano is a world class DM, period. Guys like him who has so many caps for a leading football country at his age, don't come by that often.
Mascherano wants to play for us, and only us in England and he wants to prove to everyone he can cut it in England, so his attitude is spot on.
Rafa wants him, and his performance on the pitch has proved that he adds more value to the team than Momo (which I rates, but I will pick Masch over him at this moment for the majority of the games).
He proved that he can stop the likes of Kaka, and to me Masch is like 'Kaka' when it comes to Defensive Midfield in the world. And if we pay 37 million for Kaka, I don't think anyone will complain that we should save that 37 million for a CB and a winger, since we already have attacking midfielders like Gerrard / Benayoun.
He is THAT good. As per if he is worthed 17 million, how much did Man Utd paid for Heagreaves?