Six years have past since Limbo was first launched on Xbox Live Arcade, and to this day it remains one of the most popular indie games ever released on a console. Naturally Danish developer Playdead wanted to do a follow-up, but despite the more than half a decade wait almost nothing has been seen or heard of it until very recently. It was at Microsoft’s E3 press conference though, where it was described as a classic in the making. And they may not be far wrong.

Inside might have been at E3 but if you watched the pre-show event (or the video below) you’ll know it was only shown for a scant few minutes. There are a few obvious reasons for that, perhaps the most important being that this is a game where those that have played it are desperate not to spoil it for those that haven’t.

The game begins in what looks for all the world like a current gen remake of Limbo: you’re controlling a small boy as he runs from left and right across the screen, through an ominous looking wood. There’s never any explanation for what’s going on, or any dialogue, but in the background you can see people being rounded up and transported in trucks and trains in a manner clearly meant to be reminiscent of the Holocaust.

The boy is being hunted by soldiers and tracked by dogs, both of which will murder him in a disturbingly violent manner if they catch him. But the game does not evolve along the lines that you might suppose from the opening minutes, and instead the ruined farms and a strangely aggressive pig offer the first real clues as to what is going on. By the end of the game your expectations have been turned on their head and… you’ll be left with far more questions than answers.

In terms of gameplay Inside is a 2D platformer, just like Limbo, but with a new emphasis on stealth and a more varied and complex puzzle element. Objects in the background (dogs sprinting down a corridor towards you, men shining torches to spot you) often interact with you, but you can only run left or right. And since you’re just a small boy you’ve only two actions you can perform: jump and grab objects.

Despite this, the puzzles get very complicated very early on, as a steady stream of new concepts are introduced the more you explore (we’re trying to avoid spoilers here, especially as the trailers don’t really give anything away either). Given your limited abilities they almost always seem impossible as you first consider them, before a spark of inspiration makes you realise the answer should always have been obvious. We’d argue that the game’s ability to keep doing this, from the first moments to the very ending, is one of its greatest achievements.

But as good as it is, Inside can be a very frustrating experience to play. The platforming elements are never very taxing in themselves, but they can become irritating when they’re mixed with timed challenges and puzzles. It’s common to have already worked out a puzzle but to slip up on some minor timing element and have to repeat the whole thing again, when really you just want to move on to the next set piece.

This doesn’t represent any great failing on the part of Playdead but it does make it more obvious than it might that the game is extremely linear, and apart from the odd diversion you’re having to follow the story and action in exactly the way that the developer intended. This was an issue with Limbo too, but where Inside has an additional problem it’s that there’s no equivalent of the giant spider from the first game – to act as a recurring menace and visual anchor. Inside doesn’t quite have the same dreamlike atmosphere of Limbo and yet in many ways the concepts are a lot stranger, which creates a tonal mismatch that steadily increases as the game goes on.

And while this isn’t a fault, we also feel compelled to mention that the experience of playing Inside is often an oppressively bleak and depressing one. Purposefully so, and to make a serious narrative point about empathy and conformity, but watching a small child being speared through the chest or torn apart by dogs is not the sort of gaming experience to please everyone. Even if it’s never very graphic.