The Celebrity Reflection that arrived at PortMiami last month had changed so much from the original ship in its class that it was two feet wider in order to balance the weight of an additional deck and other new features.

Carnival Breeze, which also arrived last month, is only the third ship in the Dream class, but its public spaces are very different since they incorporate features from Carnival’s new Fun Ship 2.0 program, launched after the first two Dream-class ships were built.

Both are the last ships in their class.

Of 2012’s three new ships, only Oceania’s Riviera is not significantly different from the first ship in its class. Frank Del Rio, chairman and CEO of Prestige Cruise Holdings, Oceania’s parent company, says he’ll use the same design to build the next Oceania ship, although that will be at least two years off.

In the world of cruise ships, the end of this year will mark a graduation of sorts. Most major U.S.-based lines have wrapped up one ship design and are moving on to a new one.

Why? Guests demand changes, technology allows for features that didn’t used to be possible, and ships need to keep up with the competition — or get out in front of it.

The result: Ship designs are more fluid; there are more differences between ships built from the same basic blueprint, and older ships are sent into dry dock to be retrofitted with features from newer ships.

Among the features on the last class of ships that seem to be keepers are more elaborate water parks and sports decks, Norwegian’s cabins for the solo traveler, spa-linked staterooms, exclusive luxury areas on non-luxury ships, more niche bars and ever-more-specialized restaurants.

“One thing they all have in common is increasing options, especially for dining and drinking,” said Carolyn Spencer Brown, editor-in-chief of Cruise Critic. “Norwegian Cruise Line has been the innovator here, and now others are following suit in significant ways. It’s recognizing that travelers don’t want to be limited to set dining hours.

“Definitely the increasing use of outdoor spaces during the night as well as the day is a really great new innovation, a nice change from the days when people went inside at sundown. Princess Cruises gets a lot of credit for jump-starting this; its Movies Under the Stars has led to other really cool uses, from Celebrity’s Lawn Club (where live jazz, under the stars, is a highlight) to Royal Caribbean’s high dive acrobatics and its Central Park.”

Ship design changes reflect the lifestyle that passengers have on shore, Del Rio said. Just as homes are bigger than they were a generation or two ago, his line’s ships are bigger and so are staterooms. Dining is healthier and has more of a gourmet flair, the ambience and dress are more casual, and the stateroom has more amenities.

Carnival already has a larger ship with a new design on order. So do Princess, Norwegian, Royal Caribbean and Holland America. Not all the old blueprints are being thrown out. In addition to its two new “Project Sunshine” ships on order, Royal Caribbean is negotiating for construction of a third Oasis-class ship, the mega-ship that carries 5,400 passengers, to be delivered in 2016.

But most lines are looking for change.

“We’re always looking at how to improve,” said Gus Antorcha, Carnival’s senior vice president for guest commerce. “Guests are expecting more. They expect more choices and they expect more value from their vacation. That has really forced us to think a lot about the product, how to keep pace with consumer preferences. With Fun Ship 2.0, that’s what we have been doing. We have been focused on improving the dining experience, bars, entertainment, and the outer decks.