There are moments of astonishing beauty in pirate adventure Sea of Thieves. As the sun falls, it becomes a giant fireball on the horizon, silhouetting the craggy cliffs of some distant island. Although the visual style is painterly rather than naturalistic, it gives each moment warmth. You may not feel as if you’re really out on the open waves, but you wish you were.

There are plenty of moments like this if you play for a while. In Sea of Thieves, you spend much of your time on the ocean, sailing between the desert islands. It’s currently a game about fetching stuff. You begin alone, with a single crew member or as a squad of four, and then you’re out into the world, taking on jobs for the seafaring organisations that set up tents at every outpost. For the Gold Hoarders, you’re looking for buried treasure; for the Order of Souls, it’s the skulls of defeated foes; for the Merchant Alliance, it’s ferrying goods – mostly animals – from one place to another. The jobs are always the same: accept the mission, find the island, do the task, return to an outpost, collect payment.

The first challenge is mastering the ship. Sailing is deliberately analogue. One person steers, one navigates, someone mans the sails or loads the cannons. Once in a while, you’ll spot a sail on the horizon and know that a battle with a group of strangers is likely. These are intense encounters, cannonballs flying, crew members sneaking aboard each other’s vessels to cut down foes with swords or pistols, treasure chests being spirited away, hulls bursting open and taking on water (which you can then drain by the bucketload). Sometimes there are bigger events: the tentacles of the Kraken erupt from the foaming seas, or a skeleton fort opens up, its treasure room loaded with booty. To face these challenges you may need more than one boat, so uneasy alliances form. The potential for moments of great bravery – and of outright hilarity – is ever-present.

When you’re playing with others (and Sea of Thieves is only fun with other people – alone, it is entirely flat), you need a headset with voice chat capabilities. Though there are emotes, visual gestures and simple statements, most of the appeal of the game is lost if you can’t communicate – because Sea of Thieves isn’t really a game about finding treasure, but about messing around with other people, bellowing and following instructions, experimenting with group strategies and laughing together when something goes horribly wrong. The experience is best with friends, although once in a while you’ll pick up a crew of strangers and everything will click. The fun-to-boredom ratio of this may remind older players of using internet chat rooms in the late 90s.

There’s a chance you’ll laugh more in your first three hours with Sea of Thieves than you’ve ever laughed with a game before. We’re already seeing thousands of these little moments hitting YouTube – all four crew members playing the accordion while the Kraken attacks; firing each other from the cannons into a skeleton watch tower; chasing pigs through the trees while drunk on grog; accidentally leaving someone on an island.

But then … the allure fades. There is no progression in the game – you can’t buy better ships or weapons. In a way, this is a good thing: everyone enters the game as an equal, whether it’s their first time or their 1,000th. But the bigger problem with Sea of Thieves is that the islands, little knuckles of sand and grass jutting from the waves, are all extremely similar, and they all feel empty. There are little tasks and secrets hidden around the world, but not enough that you can just set sail and find a surprise. The only non-player enemies are skeletons, and though there are different sorts, with different abilities, after a few hours you start yearning for something new.

There is a vast and complicated argument about longevity and value in the video game industry. It is very strange to see players complaining that they’ve had hours of hilarity and joy with Sea of Thieves, but feel it is not a good game because now they’re bored. Those hours are worth something. This is a game where the whole lore, the whole purpose, the whole backstory, the whole future, is shared between the players – in Sea of Thieves, the burden of design and experience is on us. For better or worse.

If you have Game Pass, Microsoft’s monthly subscription service, Sea of Thieves is free – and a must. You’ll have moments in this game that you’ve never had in a game before. If you’re buying it outright, you may want to wait, because Rare will surely start building on these promising foundations.

It is no wonder Sea of Thieves has drawn comparisons with No Man’s Sky – at its best, when it’s firing on all cylinders and you let yourself sink into its peculiar vision, it is majestic. The glint of the sun on the choppy waters, the friend who always gets lost in the caves, saving a hold full of chickens from drowning, standing on an island after a battle and watching your ship sink beneath the foam. These moments are the treasure. But are they enough? The problem is not only that there’s too little to do; it’s that you want so much more.

• Sea of Thieves is out now, £49.99; free with a Microsoft Game Pass subscription.