From what I can tell, there are 3 main classes of stateroom (not including concierge), with the primary differentiation being on size.
Inside staterooms are Standard (Cat 11, 169 sq. ft) and Deluxe (Cat 10, 204 sq. ft.)
Oceanview staterooms are Deluxe (Cat 9, 204 sq. ft.) and Deluxe Family (Cat 8, 241 sq. ft.)
Cat 7s are 246 sq ft Deluxe Oceanview with Navigator's Verandah (i.e. a smaller, obstructed-view verandah).
Verandahs come in Deluxe Oceanview (Cat 5 and 6, 246 sq ft.) and Deluxe Family Oceanview (Cat 4, 299 sq. ft.). Note that verandahs are included in the square footage total.
Generally speaking, the letter designation (A, B, C, D, E) indicates relative quality or location within the category, but there are a few exceptions:
Category 8A cabins have the same square footage as the other 8s, but are more square-shaped than long, have 2 large portholes, and do not have a split bath. They were originally intended to be handicap-accessible rooms, but not all of them turned out that way.
Cat 4E and 5E cabins have an oversize verandah, some of which have whitewalls.