Parkour, or free running, serves as a primary inspiration for Mirror's Edge. The construction of another way of looking and moving offers the first means to adapting that activity: like the skateboarder, the free runner sees the world differently: as a set of affordances for previously unintended means of locomotion.
But there is something else about parkour that Mirror's Edge translates deftly: a sense of fluidity. The free runner does not simply see the city differently, he sees it as such without hesitation, moving immediately from step to wall to landing to ledge to ground. This sense of effortless continuity is what makes parkour beautiful to watch and, I presume, gratifying to experience. Not only must the successful free runner make alternate use of familiar surfaces, but also he must do so as smoothly as possible.
Mirror's Edge deploys two main strategies to create the experience of fluidity. The first is its first-person perspective, an unusual, risky decision that alienates some players, those unable to get over the fact that Unreal Engine 3 would have afforded a more straightforward third-person viewpoint. The game would indeed probably have been easier to play with the camera locked behind its main character, Faith.
But the game's purpose was not to make movement predictable and easy -- to make it transparent, in the lingo of HCI. Rather, Mirror's Edge attempts to create a sense of vertigo which the player must constantly overcome in order to reorient Faith toward her next objective. The rewards for success are remarkable: running to a sprint and properly vaulting a fence produces a sense of physical mastery commensurate with the parkour expert.
The second is its unusual level structure, one designed for difficulty. Mirror's Edge is a hard game; the number of times a player, even a good one, will fail is utterly enormous. When such failures occur, the game often asks the player to restart from a particularly punitive location, demanding that he work back to a point where, inevitably, he is likely once again to tumble violently down to earth.
Unlike Assassin's Creed, which adapts the fluidity of parkour by making movement consistently easy, Mirror's Edge adapts that fluidity by making it hard. But what initially seems like a punitive design gaffe actually carries a crucial payload: requiring the player to reattempt sets of runs insures that the final, successful one will be completed all in one go.
This is not the same type of frustration that one finds in Mega Man: the punitive levels are not conduits for final accomplishment and trophy, but for mastery over the very process of moving through the levels themselves.