Most puzzle games on iOS are built around a central mechanic.
Whether you're digging out tunnels in Where's My Water?, positioning torches in Helsing's Fire, or cutting the rope in, erm, Cut the Rope, the best phone puzzlers take one idea and then twist it and spin it in all sorts of different ways.
But monochrome puzzle-platformer Limbo refuses to be a one-trick pony. It's constantly surprising you with fresh and original ideas, and an endless parade of beautifully engineered puzzles.
If you aren't pressing forward to see where the game's understated narrative will end up, you'll be pushing on to see what challenge is awaiting you around the next corner.
How long can you go?
The puzzles range from the humdrum - shifting crates to clamber up ledges and swinging on ropes to hop over traps - to the fantastical - anti-gravity machines, movement-restricting brain slugs, machine guns with laser trip wires, and entire rooms that spin in circles.
They're thoughtfully designed, and stump you for just long enough to make you feel like a big old clever clogs when you finally solve them. But here's the kicker - the puzzles often only reveal their secrets by killing you.
A saw blade effortlessly slices through the protagonist - who happens to be a wiry little boy - and suddenly you have an idea as to how you'll overcome it. Next time, that is.
Over the course of this moderately long adventure, your hero will likely end up beheaded, crumpled up into a lifeless pile of bones at the bottom of a bit, and chewed up in the frighting snap of a bear trap, all in pursuit of the next puzzle solution.
Stuck in purgatory
This constant death can be frustrating. And it feels like the game is committing some cardinal sin of game design. But it fits the game's sick and twisted style; its grisly pitch black humour; and its macabre sensibility.
This is a game where you use the bloated corpse of a dead child to cross a river, and where a malicious troupe of wild children pepper you with blow darts. It's a morbid game, and that point just wouldn't be driven home if you didn't get impaled by a giant spider's leg every now and again.
That dark style is mirrored in the aesthetic. Everything is painted in black and white, with foreground elements drawn in stark silhouette, and background art covered in a thick mist. And even though everything is monochrome, Limbo's three environments (an eerie forest, a ghostly noir-like city, and a disappointingly dull factory on the fritz) have their own sense of place.
Doesn't matter if you're black or white
The boy is well animated, too. He has a real weight to his movements, and a sense of inertia and acceleration when he moves, which makes him feel like a human being that you care about. Even if he is a silhouette with two white pinpricks for eyes.
Controlling the little lad feels natural and easy, and there are very few moments when you even need to think about the controls. One thumb handles movement, while swiping the other makes him jump (and tapping makes him grasp hold of levers).
Plus, continuing the original game's quest to have absolutely no clutter on the screen, the virtual joystick and all buttons are completely invisible. Even the 'pause' button is hidden until you start thumbing around at the top of the screen.
Limbo is a brilliant adventure, because it's always surprising you. It surprises you with every new puzzle idea it dreams up. It surprises you by how morbid it can be. It surprises you when your hero is snapped up by a bear trap. And this iOS version is surprisingly faithful to the XBLA original.