There’s a tension in every open-ended game (or even every game, period), a tension between avatar and surroundings, figure and backdrop, between the simplifications which allow players to interpret and act upon the world they’re given and the fertile, vital unpredictabilities of that world – in short, between the rules of ‘gameplay’ and the ruled-upon ‘setting’. Faced with so challenging a dichotomy, many developers lean one way or another. The randomly generated ASCI landscapes of cult hit Dwarf Fortress are famously more than a match for their colonists, for instance, while Jak II’s capaciously chunky steam-punk environs are quite passive, sterile, despite their graphical liveliness.

Ubisoft Montreal’s Assassin’s Creed series tackles this tension head on, and therein perhaps lies its claim to greatness. Where other third-person sandboxers cloak the enmity between order and chaos in make-believe, Assassin’s Creed transforms it into a component of the make-believe, a premise. Your character, Desmond Miles, springs from a long line of assassins, each engaged in a shadowy war with the Illuminati-like organisation known as the Templars. To penetrate the centuries-old mysteries of Abstergo, the vast military-pharmaceutical corporation the Templars have become, Desmond must tap into the “genetic memories” of his ancestors – 12th century Arabian backstabber Altair in the first game, Renaissance nobleman Ezio in this one – reliving their thoughts and deeds with the aid of a high-tech VR machine termed the “Animus”.

I've been to Florence. The Duomo looks even better when you're standing on top of it.

What this effectively means is that the game’s rules, regulations and – of course – limitations exist as a game within the game, “externalised” for consideration in the form of the Animus’s mechanisms and interfaces. It’s an elegant transposition of a key design concern – elegant enough that we can overlook both the contrivedness of the temporally riven plot and the present-day cast’s painful lack of charisma – and one which underlines the assuredness with which Ubisoft has mediated the conflict between gameplay and setting.

“Eagle vision” encapsulates this mediation rather handily. Approach a busy thoroughfare in Venice from aloft and you may struggle to make sense of it: the developer’s fidelity to the original clothing styles, building materials, types of shop and social mannerisms is as impressive as before, and while the engine is a few steps behind the times (tearing, pop-in and frame-rate drops are all very evident) it pushes out a respectable level of detail. Hold down triangle, however, and the Animus will dim the global lighting, strip out the rich yet impractical distractions and swathe enemies, friends and objectives in shimmering, arcade red, blue and golden auras.

Enemies now poke through haystacks when alerted. Fortunately, you can return the favour.

The mostly unchanged free-running mechanic works on the same principle of equilibrium. Hold R1 and X button down and the Animus will take over the business of picking and gripping individual handholds or leaping from beam to beam, leaving the player to handle broader questions of high road or low road, whether to scurry along a clothing line or leap from a fluted stone pillar, whether to make use of the side-route subtly advertised by a cluster of pigeons or carve out a path of your own.