Being as big a fan of Firefly/Serenity as I am and mostly enjoying Buffy/Angel as well, I used to give Whedon slack on Alien 4. Hey, that big mean studio and bad, bad French man, and mean old actors screwed everything up.
Hell no. Last time I watched 4, I paid attention (The pain! But that's beside the point...) If his script is still mostly intact, it still makes for an awful Alien movie. Y'know why? Them damn jokes. The ultra-witty work fine for Buffy and Firefly, universes of Whedon's creation where mankind has mutated into a strange, super-snarky doppleganger of itself, but it's just no damn good for an Alien movie. Thing's have got to be straight and reinforce the dread, and you just can't do that while your heroine is cracking wise in the face of certain death.