[Sekto Springs]

Try and imagine Little Big Planet with flick-screen and see how much you want to play it.
A sidescrolling environment will full atmospheric fx and interactive background elements is far more enthralling than walking through several linear, static matte paintings. Also, bear in mind that 2.5D is in fact 2.5D because there's a shift in perspective as you move, like a real environment. Would your perspective reset itself with each new screen? That doesn't sound slightly irksome?

But I digress, this is an HD remake of AO, not a complete re-do. Maybe they will keep the flick-screen for the sake of not diverging too far from the source material. It's just that given the state of games today, I don't think 2.5D flick-screen will really fly with anyone who hasn't already played the originals.