Claiming the title of biggest cruise ship afloat, the new Harmony of the Seas is also home to the longest slide at sea. But what is it really like to sale with over 6,000 passengers? Sue Bryant finds out

I’m staring in to the Abyss. The Ultimate Abyss, the longest slide at sea, on the newest, biggest cruise ship in the world, Harmony of the Seas. I don’t like heights, so the glass platform on which I’m standing, 16 decks up, is a big challenge. I shuffle onto my mat, trembling, wait for the green light to say “go”, take a deep breath and launch myself into space.

I zoom through blackness, screaming like a banshee. Bright disco lights suddenly flash and spin around the metal tube and I’m circling, shooting out onto the Boardwalk, 10 decks down, whooping and yelling. It’s 14 seconds of pure adrenaline.

And this just about sums up Harmony, which is touring the Mediterranean in its maiden season before heading to the Caribbean. One big thrill ride and a lot of dazzle.

Royal Caribbean has taken the best of its two giant Oasis-class ships and thrown in some elements of the newer Quantum-class on this 227,000-ton behemoth, which is a whole 33cm longer than its nearest sister, Allure of the Seas. Anybody familiar with Oasis or Allure will discover familiar features such as an ice rink, the outdoor AquaTheater, where audiences are thrilled by high-diving displays, a zip line, the leafy Central Park, with more than 10,000 trees and shrubs, and posh restaurants sitting alongside swish stores by Bulgari and Cartier.

Features that have been inspired by Quantum of the Seas and its sisters include the Bionic Bar, a whizzy cocktail bar tended by two dancing robots, a Jamie Oliver restaurant and inside cabins with virtual balconies that show real-time images of the outside world on a giant screen. Then there’s the new stuff, not least the Ultimate Abyss, which attracted big crowds when I was on board. The children’s club, Adventure Ocean, is even better than on the other ships; kids even have their own very cute little theatre and a science lab.

Harmony needs to be approached as a massive, floating resort that happens to visit a few ports of call rather than an ocean voyage during which you commune with the sea. It’s busy, noisy and colourful and not very ship-like. A crewmember told me, “The first day is crazy, while everybody finds their ‘place’ on the ship, and after that, it all settles down and you wonder where everybody is.”

He’s right. My favourites were the adults-only Solarium, a peaceful place to read and snooze, and the cafe in Central Park. I loved Wonderland, a two-deck fantasy world of superb molecular cuisine and a super-cool cocktail bar, with stunning views down over the Boardwalk. The halibut baked in paper, and molten chocolate pudding with liquid nitrogen pistachio ice cream were both exquisite.

Royal Caribbean is famed for its ambitious Broadway hits and the headline show on Harmony is Grease, which has been adapted from the film and the stage show and sizzles with energy. At the first showing, the whole audience was on its feet. Throw in the ice shows, the AquaTheater, the comedy club, a very classy jazz club and live bands and the amazing value of this ship becomes apparent, as none of this costs any extra.

So we’ve told you a little about Harmony of the Seas. Now check out the gallery to see what else is onboard.