I think the original one in NYC is the best. That place is outstanding - all the time. But, expense account only in terms of budget.
I have eaten at the Las Vegas outpost of Il Mulino, and while the food was just good - the price was still astronomical. We had shrimp orgenata, which was standard. I has a gnocchi dish with a pancetta cream sauce which was very, very good (but heavy).
I think that as it expands, people expect it to be the same as the original and I'm just not seeing it live up to that yet.