I don't know... I have made good ones, but never really achieved the mind-blowing levels of some that I've had in great restaurants.
For me, I think that the exceptional ones I have had, involved a demi-glace, which I have never made.
I had a friend who was a chef at a restaurant in Laffy named Spazio Tratorria, which had a ridiculous Osso Bucco w/ Demi-Glace. He said that it took 24 - 48 hours to make the demi-glace. It involves roasting beef/veal bones (dry) on a baking sheet, and deglazing the baking sheet, etc., etc. Stock, reducing, butter, reducing, wine, reducing... you get the picture.
Needless to say, I have never committed to that kind of effort when I made osso bucco, but OMG.