Since you're familiar with Disney, one small difference in the MDR menus is that Disney splits the starters into a soup/salad category and an appetizer category and the servers will ask you for your choice of both. Royal however has just a starters category, including the salads, soups and appetizers, implying that they expect most people to order just one. As others have mentioned, however, you're more than welcome to order more than one if you wish.
Another difference is that Royal has some MDR items which are on the menu every night ("Classics") along with items that change from day to day. Also there are a few "extra charge" entree choices.
If you go over to the Live Blogs section you should be able to find many pictures of menus, both for MDR and specialty venues.
MTGill got a reaction from Sackboy in First ever RC cruise, need tips