While there are usually good things happening with melting cheese - I find that in almost all cases (save blue at least) flavor is pretty much eradicated.
I use a sharp cheddar from Somerset, England with a great 'bite' and when used for a melted cheese sandwich or on a 'cheeseburger' it becomes almost totally neutered.
The same seems to be true for parmesan, aged gouda, mature emmenthal, etc.
Yet the net seems to be filled with raves for how melted cheese has infinitely better taste than 'un' . something I don't agree with at all.
And this does call into question - for me at least - the big deal about the whole 'au gratin' deal in cooking.