It only takes one Alien. That's what everybody seems to forget. Like an Anthrax germ smeared into a stranger's handshake, one Alien can reduce an entire civilisation to a handful of mewling apes, cowering in the corners of acid-eaten vessels. Turn that primeval death-dealer into a pack animal, as James Cameron did with Aliens, and you risk diluting it, reducing it to an expendable asset. Cameron found a balance, in the end, but the same can't be said of his countless imitators, among them the folk of Gearbox Software, developer of last year's woefully ramshackle and attrition-driven Aliens: Colonial Marines.