The length of a movie is nothing...if you want the spectators to care about the characters and the situations depicted, you need one and a half-two hours movie...if all you want is an action movie with no time wasted on characterisation, then 100 minutes is enough...provided the characterisation you do is good enough to make one care about the characters. From the looks of it and given the directors involved, i think this will be a sequel that will try to correct the so-called 'mistakes' of the original, with a cast of unknowns in an arguable setting, reducing the number of Aliens and Predators...which can make it more focused or give away the guys in rubber suits...Given the novice directors, I wouldn't hold my breath...