For me, It is the lack of respect for the creatures, from the designs to the mannerisms. I mean, when I'm watching Predator 1, at the end where we first see the Predator decloaking coming out of the water, It freakin looks like a real, other worldly alien that makes you afraid. Then, when he removes the Biohelmet and we see his face, it looks real, resembling a crustacean/mandalorian warrior. Even the way his mandible kinda twitches. Every frame of AvP looks like an actor in a latex rubber suit. Then when we actually see the face,...umm, did someone forget the Predator's contacts?! Remember the scene where Celtic and Chopper "fight" the Grid Alien? My God, that looked like a stop-motion cartoon! Many other scenes just threw established canon out the freakin window! Example: Anytime could jump from tree to tree like he defied gravity. The end scenes where he is coming to fight Dutch, he leaps from tree to log bridge like he was flying. Scar looked like a wrestler struggling to walk in his costume when he jumped. When he helped Lex pull the chain attached to the Queen, he looked like he had the strength of a 12 year old.
I would like to say what happened in AvP-R, but most of the time the bad lighting kept me from seeing the action. The setting was all wrong, with the crappy kid actors. It had too much of a Scream feel to it. Honestly, a few of the Wolf/Alien fight scenes were pretty good.
The Brothers offended me from the start, just like RR did with Predators. They both complained about the their predecessors and promised that their own film would be the ultimate one that would make you forget what came before them, as though they were the saviors of the franchises, taking liberties with sound clips and homages at their will!
Finally, I never have understood how the Predalien, which I absolutely HATED, grew to full size so FAST!! At the end of Avp, the ship is leaving Earth, and it bursts out and within a few seconds it is full size killing Elder predators, causing the ship to crash back to Earth. Either the pred ship takes a long time to leave the atmosphere, or it was circling the planet a few times, which wouldnt make sense.
And yes, I own them, and will watch them occasionally, but the whole time I'm wishing the costumes werent so fake, and the Aliens werent just target practice.