For me, Elika takes the frustration out of the experience and allows you to concentrate on exploring and experimenting, finding new routes and new areas and just enjoying the ride. There's still enough skill in timing the moves to make you feel like the acrobatic hero, but you're rarely playing the same five minute stretch over and over and over again because you can't make that final, fearsome jump. Prince of Persia isn't just a game you want to complete; it feels like a game that you will complete - and I couldn't always say the same about The Two Thrones.
Elika's powers are also key to how the new structure works. Basically, the hero and the princess are up against an ancient, evil god, barely restrained by a series of 'fertile grounds' that give life to the city and keep him firmly under foot. Sadly, a disastrous choice by Elika's father has allowed this god, Ahriman, to unleash his dark force, an inky filth known as 'the corruption', on the world. Basically, our heroes have to get to each fertile ground and reawaken the energy stored there, replacing the corruption with life (in an effect that will be familiar to fans of Zelda: The Twilight Princess or Okami). However, while the first few grounds are easily accessible, the remaining sites require Elika to master four additional powers. These allow Elika and the hero to run up vertical walls or take flight from certain pads, but to gain them you need to gather light seeds and take them to the central temple. Unfortunately, these light seeds only appear when an area is cleansed of the corruption.
Were I feeling mean, I'd say that this was a cheap way to extend the game's lifespan by forcing you to redo sections you've already done, but in fact I'd go the other way: gathering light seeds gives you a reason to really explore areas you've earlier rushed through, and each has enough secret pathways to make the effort worthwhile. What's more, the levels - all rather dark and cold when under the influence of Ahriman - are just beautiful when restored to their natural state. When you get to a high spot and gaze far across the city, looking at the windmills of the construction works or the high towers of the palaces, the impact is simply breathtaking.
I'll come straight out with it: I love the new Prince of Persia. It's beautiful, engaging and superbly entertaining, and the plot and characterisation work brilliantly. Admittedly the hero starts off as a slightly irritating character, but he soon develops into a more interesting Han Solo-style rogue. And while his relationship with Elika doesn't have the poignancy you get from the more protective link in Ico, it still adds a real warmth and personality to the game. The open structure has consequences in terms of maintaining some progress in the difficulty level, but the game gets around this by introducing new elements of corruption like poisonous clouds or grasping tendrils that make otherwise easy stretches that bit more tricky. For most complaints you think you can see coming, Ubisoft's team has found some way to head them off.