This might mean, for example, that you don't have enough power to perform that big jump at the end of the rooftop cleanly. You'll still make it but only by grabbing the ledge, and you'll lose a split-second as you have to pull yourself up. Similarly, it's important to perform a barrel roll with perfect timing when you land from jumps. Mess it up, and Faith will need a second to right herself - and you'll have lost all that momentum.
But even if you pull off a perfect chain of moves from the start of the course to the end, you won't get the fastest time if you haven't plotted out the best route. This is where the Time Trials have an action-adventure flavour you won't find in racing games. At the end of each trial you'll be told the distance you travelled, and the minimum distance you could have travelled had you taken the best possible route. The distance between these figures is often astonishing. You might be ever so proud of the shortcut you found round the back of that building, that secret jump that saves whole seconds and the hidden zip-line you discovered - only to find you're still covering a hundred metres more than you need to. And you have no idea why.
The result is that while you're repeating courses, you're not only practicing your moves but looking for new shortcuts and better routes. This makes the Time Trial courses more than just a test of how good you are at pressing buttons, and consequently more interesting. It also increases the incentive to repeat them over and over again, as does the star rating system. The only way to achieve three stars is to find the perfect racing line through the course, to work out the best moves for navigating your way through it, and to pull them all off flawlessly.
Which is by no means easy. Sometimes, for example, it's just impossible to see how you could reduce your distance travelled. At this point you might want to cheat, and download the ghost of someone better at the course than you. Then you can race against the ghost, and more importantly, see the route taken to get that super-fast time. You can also race against your own ghosts, which is a good way of spotting ways to improve your efficiency.
Not all the courses place an equal emphasis on route-planning and acrobatic precision. In another one we tried out, Stormdrains, there's only one pathway through most of the course - and it involves traversing a series of elevated platforms. There's very little room for error; if you miss a single jump, your only real choice is to start the whole thing again. However, the restart mechanism is fast enough and the courses short enough to prevent this from becoming too much of a chore.
The question is whether the Time Trial mode is good enough to provide long-term entertainment, or whether it'll feel like a tacked-on extra. That will partly depend on what kind of player you are. Those who have the patience to achieve perfection and get a thrill from topping leaderboards will probably find it has plenty of appeal; those who are more Mario Karters than Project Gotham Racers might not.
In any case, an even bigger question still hangs in the air: will Mirror's Edge really be as amazing as everyone hopes? Fortunately it won't be long before we can tell you once and for all, with just under a month to go until it's on shop shelves. For now, though, it's clear that DICE has thought long and hard about how Mirror's Edge can draw influence from other genres, and still offer something different.
Mirror's Edge is due out for PS3 and 360 on 14th November.