I think there are many reasons to dislike the movie.
It had a small budget and it shows. Many disliked the earth setting and for good reason. It just does not feel right.
Some new additions to the lore were more than questionable. For example the predalien chestburster barfing.
The movie was too dark.
The human element of the story was a drag.
The fights, the titular alien vs predator, were more than underwhelming.
The cleaner angle just does not work for me. It just makes no sense that you have a predator running through town, trying to drop his desolving liquid on every trace of the aliens while the whole infestation is spreading...before the humans realize what is happening. How in god's name should that ever work ?
There was only one predator, so the outcome of every battle besides the big final one was never in any doubt.
The aliens... i have no problem seeing a skilled predator dispach aliens but the way they did it in the movie was horrible. There is just no sense of threat from them after the first encounter in the sewers. You feel the aliens just forget they have limbs and a tail whenever they are in melee with the predator and take their sweet time waiting until he finishes them.
It's just not a good movie. I really struggle to see how anybody could see it differently. Sure if you like the movie, by all means enjoy it. I just can not understand why. Even if you just want to see the predator kick ass in a cheap B-movie i can not understand how what you got satisfies you. Would you not like to see an actual fight with a worthy opponent? The fight scenes in the movie don't elevate the supposed elite predator, it makes him look lucky that he was up against such wimpy opponents. The alien in the first AVP and the supposed inexperienced predators from that movie looked like they could beat the shit out of the Requiem predator in comparison.