Like so many, who know better than I, have said, there have to be boots on the ground. But...they need to be local boots. Kurds, Free Syrians, Jordanians, Turks. Our job is to support them,
I sort of disagree, I think that to clean the area out, and get back to some resemblance of control there needs to be a large professional western force.
The only way to regain control is with a large campaign with all the sustained boots on the ground and logistical support which go with it.
Though some of the surrounding countries have such forces (to what degree is to be debated), the political reality of operating in Sunni areas is problematic.
Having a pile of Westerners go in defeat ISIS (relatively speaking), followed by a large force of peace enforcers from surrounding countries would be the best bet.
A sort of bad cop good cop thing. It is likely the majority od Sunni's don't like ISIS, but also don't like being "occupied". So you need to decrease the annoyance factor.