3 out of 5 from Joystiq. sounds like the switching mechanic is pretty annoying:
There is a twist this time around, namely a timer that constantly looms over your every action. When it runs out, whichever character you're controlling immediately succumbs to a case of plot-mandated narcolepsy, and control shifts to the other in whichever world he happens to be in. The idea is for Sora and Riku to experience different parts of each world's story while swapping items and stat bonuses based on how well you perform before the clock strikes zero and you turn back into a pumpk– er, fall asleep.
In practice, however, the forced switching mechanic is pointless at best and downright obnoxious at worst. At one point, for instance, it interrupted me right as I was about to strike the killing blow on a particularly frustrating boss. The next time I took control of Riku, I had to start the whole battle over again. Pacing, meanwhile, goes out the window, with one character's moment of big drama often giving way to the other's ho-hum introduction to a world and its stiffly acted characters.