In most cases, such as a standard Caribbean or Alaska cruise the answer is no. However, there could easily be one port that does require a passport. Guests denied boarding by local immigration officials for lack of proper documents are not entitled to a refund. All guests on a Caribbean cruise that calls on Belize must carry a passport. Visa requirements vary by country and are subject to change.
Some new ships are huge.
That all depends on you. The majority of new ships accommodate 2,000 passengers or more with some accommodating over 3,000. The advantage to cruising on one of these ships is that there is so much to do and so many diversified social options. On larger ships you will find more dining and entertainment options, as well as more lounge options - which allows you to find a place suitable to your taste. On a smaller ship you will sacrifice the quantity of options available, but will notice a more relaxed, less crowded atmosphere.