To be honest, I didnt actually think we should have signed him when we did - or rather, we should have signed someone else in addition to him.
@Shyftyy in the matchday thread summed up how I feel on it quite well -
I feel compelled to defend Fellaini just because so many fans have it in for him. I am aware that I now look like the Mad Winger of the Fellaini thread, but I have never actually regarded him as being a key player for us, simply that he deserves a lot more credit than most fans are prepared to give him.
In the last month, the only player you can make a case for being more deserving of Player of the Month than Fellaini is De Gea in my opinion, but whilst folk herald De Gea as the prodigal son of Schmeichel and VDS, Fellaini still seems to divide opinion in a way that has been highlighted in this (and plenty of other) threads.
The formatting comment was meant to be tongue in cheek, also.
edit: I agree that he is better in a 3-man midfield although I could see him playing in a 2-man midfield alongside Herrera as well.