Every footfall in Braid can be undone – every misjudged jump into cannon fire, every tumble into a pit, reversed instantly. Unlike the comparable time-bending abilities in Prince Of Persia: The Sands Of Time, there are no limitations on the extent to which you can turn back the clock. You might think that this would make a 2D platformer a bit of a cinch – but you quickly realise that Braid’s challenge isn’t getting across each level but collecting the jigsaw pieces that are scattered through it, separated from you by brow-furrowing temporal obstacle courses.

Despite appearances, which play heavily upon the conventions made familiar by Mario, Braid is really more a puzzle game in the vein of Portal – and, it turns out, is no less tightly designed, no less sustained in its invention, than that title.

Each set of levels introduces a new twist, from which Braid squeezes an astonishing range of ideas without ever letting any one outstay its welcome. The first is that some items are immune to time-reversal. An early example sees you carefully rewinding to shift into phase a series of moving platforms – some normal, some time-exempt – so that you have enough evenly spaced steppingstones to cross a large gap.

Later tiers allow you to drop time wells, which slow everything to greater degrees as they get closer to the epicentre, and another duplicates the player with every branch of the timeline – a shadowy doppelganger performing the actions you did yourself before the last rewind. Perhaps the most delightful and coherently realised of Braid’s tricks is seen in the third tier, where every step towards the right advances time in the world around you, and every step left reverses it.

Braid teaches you to understand the behaviour of these mechanics, and then ratchets up the convolution their usage requires, culminating in those exultant ‘ahhah!’ moments that are the hallmark of a superb puzzle. Only once or twice do they feel wanting. Sometimes you’ll work out the solution only to be repeatedly foiled by over-fussy platforming and, very occasionally, paradoxes create situations which, while consistent with the rules of the world, results in objects betraying visually jittery behaviour.

Such moments of questionable design are rare, and Braid triumphantly proves that the 2D platformer can be much more than the sum of its Goombas; more than a succession of pitfalls and traps. Where it stumbles, however, is in its storytelling – a somewhat awkward text appendage to the action, written in an impressionistic style that feels a little trite in its self-conscious obscurity. There is an attempt to reflect the story’s themes in the game design itself, but this is only really successful in the very final level, which underscores just how much more powerfully an idea can be expressed through the mechanics of play. It’s a disappointment, but one that can be easily skipped past.

Braid remains a beautiful and brilliantly demanding game that barely contains its dense population of ideas, taking its place alongside Geometry Wars and Pac-Man Championship Edition as one of the finest original titles available on Live Arcade.

Verdict 9/10