Truly Formal Nights: Cunard has the most formal evening dress code (two or three nights of the sailing) on the high seas, a delight for those who like to dress up for an evening of dancing to a big band. It isn't white tie or black tie; it's black tie optional, which means (at minimum) dark suits and cocktail-length dresses. But, unlike on other lines, about 90 percent of the passengers comply, creating an unusually elegant atmosphere.
The Best Libraries: Queen Mary 2 has the largest book collection at sea, with professional librarians in attendance, and the space affords wonderful views of the ocean from comfy reading chairs. Queen Elizabeth and Queen Victoria both have two-level libraries.