If he can play like he did in the first 45 mins vs. Everton at home he'll be a decent midfielder for us but yeah his size does create misconceptions about what he is capable of, his thighs are fecking huge and he should be a beast but strangely he struggles to track back and doesn't put himself about as much as he should (mind you that's not helped by this perception he has with refs which means they call a foul every pissing time he goes in for a challenge).
I just don't think referee's understand the idea of Marouane Fellaini as a concept... and so just award a foul for his mere presence on the pitch.