If I may also comment and ad to Krs1300's questions.....
If the formal nights are days that we are at sea, then the first night at sea is my daughters 20th bday. We, also, were planning to do a specialty restaurant for that occasion. Do you recommend that we skip the main dining room on a formal night? Are the meals significantly better then? Is the atmosphere something we shouldn't miss? Will the formal nights theme also be carried thru into the specialty restaurants?