AR, while very different from the first three, isn't really a bad movie. Its weird, it unnecessary, and its a bit disappointing, but I wouldn't call it bad. Its interesting in an absurd, very out there way. And the Newborn design is great, given that it is supposed to be an abomination and all.
And I still don't find the first AVP to be a bad movie. It comes no where close to either the Alien or Predator films, but its a fun ride in a really cool setting and lots of cool throwbacks to the originals.
And then there's AVPR... Yeah....