Is the utter unoriginality in the designs of alien life form. Think about it, when is the last time you've seen an Alien in a movie that wasn't just a variation of a human or an animal we already know? Specifically Avatar, every creature was just a play on everything we have on Earth:
A fukking monkey with four arms
A tiger or some big wolf-like thing that roars like a lion
Big blue people with dikk-hair
Come to think of it, is it even possible to create something truly alien without basing it on an animal that already exists?
For instance, if we never discovered ocean life and only knew about land animals do you think humans could imagine a fish or an octopus and attribute all of the appropriate mechanics? shyt, probably not.