Never had the pleasure of dining at Marc's Italian Steakhouse but we ate at Mezzo several times a month when Marc was there. Parma is every bit as good and in some ways better.
The atmosphere is very casual but the food is extremely serious. Seared octopus is both tender and charred (really hard to do), the Zuppa of clams and/or mussels is the best in town, same for the eggplant parmigiana. I enjoy plain Veal Milanese, which is not on the menu but they make it for me when they have the Veal. If they have the special Wild Boar Ragu on Pappardelle, don't miss it.
This is the best neighborhood Italian that I know of in Las Vegas and we have searched! Pretty much everything is good and while not cheap, it's certainly worth the price charged. After reading this review we may go tonight, wish they had pizza a few more days a week, oh well...