I think this is the weakest of the criticisms levelled at the film; the dialogue for the co-pilots and that one line fucking flamethrower man gets are worse crimes than lack of characterisation or anything.
In Aliens you have there or thereabouts the same amount of characters. Who gets any sort of development? Ripley, Burke, Bishop, Hudson, Vasquez, Hicks, Newt, Spunkmeyer, Gorman and Apone. Prometheus has the same amount of characters, and ones you find out about are Shaw, Holloway, Vickers, Janek, Milburn, Fifield, David and to an extent Weyland. In Alien it's... the cast of Alien.
Now I think they're well rounded characters in Alien; you've got Parker whose just in it for the money, Kane and Lambert who don't really get much character development at all, Brett who's there just to back up Parker, and Dallas who is your everyday good guy stuck in shit. Even Ripley is just a tough woman in it really, none of her maternal instincts come out until she's fucking around with the cat. Ash is definitely the most interesting character.
In Aliens, you know Hudson is a fucking asshole, Vasquez is a macho gun lover, Spunkmeyer's got a stupid fucking name, Apone is a bit of a hard arse, Burke is a slimy tool, Hicks is just Dallas with a gun, Newt is a whiny kid... Ripley is definitely much better, but even Bishop is a bit of a dull character compared to Ash.
David is certainly more interesting than Bishop. Janek is no different than Parker really. Vickers is a less slimy Burke. Fifield and Milburn get the same character development as Brett does. Holloway gets short changed and is the most bland character of the whole lot, but Shaw shows more personality in this than Ripley does in the first.
It's poorly written in terms of dialogue and action, but the characterisation is no worse than the first two really.