First playthrough will probably be shy of 10 hours if you play through thoroughly looking for collectibles and stuff (going by the amount of time the game records when looking at chapter select for each stage, not sure if the game records everything including cutscenes though).
It has some extra variations on the ending though which may add some replay value if you're into that kinda thing, and you can choose different squads too, doesn't alter the experience much but I find it definitely feels worthwhile replaying it anyway.
id agree 10 hours. dont kno if that includes cut scenes or not. i played on survivor an it was about 10 hours. i only found half the collectibles tho. --- Im not gonna fight you....Im gonna kick you're ass PSN GT > JonyBeans. GO GIANTS!
I bought it yesterday and beat it in one weekend, taking some breaks in between. About 8-9 hours I would say since I left the game on. I was playing on Survivor too, searching for possible extra Nanomachines and taking time to talk to every NPC in the hub-like cities. Probably even shorter if you just did a straight playthrough on lower difficulty. --- The Storm Is About To Rage.....