The extraterrestrial sprog thing is hardly a giveaway, really. It's the curse of publicity. You know he's an astronaut, you know he flies into space where something goes wrong, and so only the lord of the jelly-heads could fail to put spaceships and unforeseen circumstances together to equal aliens.
Maybe they thought Chameleon Boy's presence would stir in a touch of enigma - and it does, to be honest. But, for an actor with Depp's range, speaking softly in a hicky accent isn't a stretch. He's more than happy to sleepwalk his way through the dopey dialogue with added astrophysics. Theron, however, comes up with a performance which should finally pull her clear of the "Statuesque Blonde" tag in the casting books. After previous underachieving/underselling (Mighty Joe Young/The Devil's Advocate), she rises above the schlocky X-Files tone by adopting an ideal survival strategy: acting.
Despite the bleedin' obviousness of the impending pay-off, the first hour is careful to keep some sense of mystery on the simmer. The NASA suits (particularly Morton) prickle with conspiracy and, for a debutant with a previous writing credit on Candyman 2, Ravich does the decent thing by sustaining an ominous low key and layering the look with a faintly otherworldly sheen. But, as the revelations flood out, he lets fly with more standard icky cutaways and some epileptic editing.
The stab at a symbolic undertone is at best ambitious, at worst wildly out of place. Theron and Depp do their best on the trust-loyalty-identity conflict, but they're crippled by the spell-breaking, screenplay-by-numbers feel of the confrontations (""I've always been there for you!"). Oddly, the pithiest line comes from Jillian's sister/counsellor Nan (DuVall): ""Men are like parking spaces. The good ones are taken and the others are all handicapped"."
Still, be thankful for the restraint shown by the special-effects department (just a few ethereal zappy things - don't expect Depp to mutate into something slimy), and all hail Ravich for avoiding the pre-adolescent gore-wankery of an infinitely more avoidable film with a similar plot... Yes, Species II, we mean you.
It's Rosemary's Alien! Depp's coasting, Theron shines, Morton is ace and there's at least an attempt to provide something a little more nourishing instead of the familiar sci-fi factory settings. Mildly entertaining and certainly sit-throughable.