AvP was not a great movie, but the worst thing about it is that it was a missed opportunity. I liked the visual design elements and there was nothing too canon-raping. The life-cycle speed-up was quite the oversight, but apart from that I can't think of anything in particular that damaged canon. Paul Anderson did not feel the need to expand upon the creatures beyond what we've seen in movies and comics already, and was happy to present his vision of the conflict. I respect that, even though he err'd.
AvPR, on the other hand, was an atrocious movie in every aspect. At least AvP had strong ties to the Weyland corporation and, while there was too much focus on the humans in many cases, especially the ones that were ultimately killed off, was about developed individuals being mostly competent. AvPR was a clusterf**k, with a zombie apocalypse setup, a teenage love subplot and enough bully-the-bully moments to make me think both directors were making up for their high school years. The Aliens were absolutely trashed, the Predators were portrayed shoddily and it was too dark to see the design elements, the pinnacle of which, the Predalien, was awful.
tl;dr AvP was poor because it didn't go far enough. AvPR hit the point of no-return early on, and didn't stop until the credits rolled.
