Alien Resurrection, in IMO had cool ideas in the story, but fell flat with the execution. I like the idea of the human DNA/Alien DNA spliced together, giving the Aliens the ability to form traps and think ahead to kill the xenomorph to use it's blood to escape. Neat ideas. But for one, they kill off the only member of the crew I liked right away, Michael Wincott's character (Can't even remember characters name). Second, I felt the first act was actually solid, but the second act just seemed flat. No surprises, no dread, no Alien kickassery. Just Newborn and an facehugger through a guys head.
One more point, the gore was over the top and just plain silly. We never saw that much blood and general goo before and felt like this aspect really stood out as why it's my least favorite of the first 4 films. I do love this film series (excluding AVP-R) and hope one day talent will return to the series with their own unique take on the story, but also take the concept seriously. That's why I think the first 3 are so great.