St Lucia is jaw-droppingly beautiful – awash with waterfalls, hideaway coves, white, sandy beaches, green-peaked mountains and therapeutic springs – yet it has always been something of a tourist backwater. But Johnny Depp fell in love with the place filming the Pirates movies, which sparked something of a charge by A-listers such as Nicolas Cage, Oprah Winfrey and Matt Dillon. Now the island’s five-star scenery has been graced with accommodation to match.

So much so that it’s home to the two hottest new hotels in the Caribbean. Some travel experts even claim that Jade Mountain, an all-suite oasis on the southwest coast, within sight of the iconic twin peaks of the Pitons, will prove to be the blueprint for hotel design in the 21st century. It opened a year ago, but it was only with the unveiling of its spa last month that it was bells-and-whistles ready.

When I arrived last week, I immediately encountered a USP. It was the first time that I’ve signed a waiver form at check-in – use of the in-room pool was an “off-limit activity”, undertaken at my own risk, with diving an “extremely off-limit activity”. As welcomes go, it was almost as charmless as the hotel’s exterior. Jade Mountain is a layer cake of concrete: it looks like an NCP car park, right down to the unfinished pillars with exposed reinforcement bars.

Inside, though, it’s amazing. Rooms are up to a luscious 2,000 sq ft in size: undoubtedly among the most enticing available anywhere. Almost half of mine was “wall-less”, open to the elements save for a discreet steel rail, and offering reach-out-and-touch, 270-degree views over the Pitons and a minty-green Caribbean sea. The soaring, 15ft-high walls were in gorgeous crushed coral plaster, the styling was zeitgeisty Asian and, of course, there was the infinity pool you’ve been drooling over in the picture above. It is hard to imagine a more beautifully designed space.

Yet I was in a foul mood. The owner, architect Nick Troubetzkoy, has been so obsessed with reinventing the hospitality wheel, he’s forgotten the essentials – especially service. Jade’s was the worst I’ve experienced in years. I arrived, as agreed, at 10am. After a series of dog-ate-my-homework excuses, I finally got into my room at 5.25pm.

Of course, even in the most well-oiled establishments, things can go wrong, but when a hotel is charging between £500 and £1,000 a night, staff should know how to handle problems with a sleight of hand that keeps guests appropriately happy for such immoderate expenditure. Here, the management’s strategy was to do a disappearing act, leaving me with ample time to stew on the team’s lacklustre performance.

No interaction with staff went smoothly: waiters couldn’t even serve lunch at the beach without forgetting half the cutlery. All they appeared to remember from the training manual was the trick psychology. One asked my room number: JD1 (at least, it would be eventually). Oh, she sighed, my favourite. Later, she inquired again: JB3, I said. Oh, she sighed, my favourite.

In Troubetzkoy world, though, I was not in a room, but in one of 24 “sanctuaries”, approached not by a walkway, but by a “bridge to infinity”. The sanctuaries are technology-free: no TVs, hi-fis, not even a phone. The idea is, you hole up and never come out. The reality is, there isn’t much to come out for – a casual dining area, a small spa and a celestial (real people say roof) terrace. Otherwise, Jade shares the unimpressive black-sand beaches and restaurants of its adjoining sister resort, the dated Anse Chastanet.

Still, such seclusion makes it perfect for some self-styled rehab. Appropriately, Amy Winehouse has stayed here. She couldn’t have chosen better – it’s practically impossible to get a drink.

To order anything, you hang out a room-service sign or press your “pendant” (real people say buzzer), and “someone comes running”. Because the technophobia extends to lifts, getting service involves staff negotiating dozens of steep steps in tropical heat, at roughly the same speed as a dying slug. After my luggage finally arrived, I needed a drink fast. It took 40 minutes.

It’s a crying shame. If Troubetzkoy had installed phones and trained his staff properly, you wouldn’t have been able to prise me out; as it stands, with apologies to Amy, if they tried to make me to go back to this rehab, I’d say no, no, no.

Fortunately, further up the west coast, St Lucia’s other hot spot, Discovery, at Marigot Bay, offers a fantastic line in unpretentious luxury – at less than half Jade’s prices. If the location isn’t quite the Pitons, the novelist James A Michener did describe Marigot Bay as the most beautiful in the Caribbean.

Despite the hotel’s size (124 minimalist rooms and suites carved into a hillside), clever layout and thoughtful landscaping keep the mood intimate; and, while you might go stir crazy in your gilded cage at Jade, Discovery is beside a marina, with shops, bars and restaurants to mooch around.

Although the resort is only a year old, it retains a good old-fashioned shot of glamour from the hotel that previously occupied the site. The celebrated Hurricane Hole bar has been restored to its former glory – in its 1950s heyday, the likes of Ava Gardner propped up its crate-barrel tables. A minus point is that the small, palm-fringed beach is no great shakes, and is a two-minute chug across the bay by solar-powered ferry. But, unlike other properties, Discovery doesn’t discourage locals from using it, thus ensuring an authentic vibe, with Rastas playing touch football and strumming guitars as the sun sets.

The down-to-earth feel also extends to the spa, where therapists pick fruit from the Zen garden for organic facials (banana is apparently nature’s answer to Botox), and every treatment after the first earns ever-greater discounts, until the seventh is free. As for service, it’s friendly, informal and blissfully efficient in comparison with its rival, which leaves me in the happy position of being able to recommend the cheaper option for a better overall experience.

— Susan d’Arcy travelled as a guest of Caribtours (020 7751 0660, www.caribtours.co.uk), which has a week at Discovery from £1,089pp, B&B, or Jade Mountain from £2,676pp, B&B, flying with British Airways from Gatwick. Or try Carrier (0161 491 7620, www.carrier.co.uk) or ITC Classics (01244 355300, www.itcclassics.co.uk)