To me, no restaurant really stands out as a must-do at MGM, but we recently tried Mama Melrose and I have to say it was pretty tasty. The flatbreads were definitely the best, and the other two dishes Fra Diavalo and Chicken Parm were good, but not the best dishes I had ever had. The restaurant had a neat decor going on, kind of a jumble of things Italian with things of California and the west coast.
Give it a try, it certainly isn't bad, and hey, maybe you'll love it!
Oh, I forgot that we also got Calamari as an appetizer which was very good, and so what the bread with the pesto and sun-dried tomoatoes that they offer.