I don't think you will get crab legs, but you will have Lobster one night and can have as much as you want. The Crab leg thing gets lots of attention cause, in the past some ships did serve them. Even Celebrity has stopped or so it appears: reason, cost! Good Crab legs are as costly as Lobster and bad Crab legs are just that, BAD. Enjoy your Lobster!!1
Good seafood (lobster) is only served in the dine rooms and specialty resturants. However, only one dine room is designated formal on Formal Night with NCL, the other remains resort casual. I also had wonderful shrimp and scallops off the buffet a couple times during our 11/02 cruise.