Everyone agrees the techniques and technologies are getting better, but they're not being used to create realistic effects.
The direction can only do so much. Hopkins created some beautiful shots of the Predator, but the closeup mask was goofy looking and the wide shot head mask didn't move properly. Those were effects problems outside of Hopkins' control. How could his direction fix a broken effect?
they did an OK job of recreating the original Predator in their sculpt of the "Classic Predator", but the movement it had was limp and unconvincing. Again, not much the director could do if the effect he's given to work with isn't done well to begin with.
Bad direction has veeeery little to do with what people don't like about Predators lately. Except for AvP, because it was Paul Anderson specifically asking for "heroic" looking Predators that basically screwed everything up on that one