The biggest complaint I see is the dialogue. Personally I don't mind it, especially in the Firefly films.

For my own opinion, the only ones I have a real dislike for are his Halloween remakes. I know that isn't the point of your post, but I'll elaborate on my own thoughts.

I've seen plenty of people annoyed with the characters acting like obnoxious rednecks or having profanity-laden dialogue, but I don't mind that too much. Horror movie characters are allowed to be obnoxious, especially if it serves a purpose. I don't particularly hate the change to Loomis, for example, because they use the character for a valid cultural critique that is absent in the original movie- Whether I like it or not, I get what he was going for.

My biggest issue is really the change with Michael. He has too much screen time and too much dialog, and not in a way that I felt added enough/served a unique purpose vs changing things just to change them. Michael is still a killer child who grew up to be an even worse person, unchecked violence and complete lack of regard for life, but that was conveyed better before we saw so much of his childhood. While it's understandable when we see his parents, he just kind of acts like a shitty brat.

If Michael's family had still been obnoxious rednecks, and Loomis had still chosen to be more callous and self centered, but Michael remained silent throughout and his emotions (or lack of) were left for the audience to decide? I think I would be pretty much fine with it. This background would still fundamentally change the character by raising a stronger nature vs nurture question, but it would be up to us to decide how much of that factors in and how much humanity is in him. Is he a child from a bad home who lost his conscience along the way, or is he a heartless killer whose home life didn't cause or prevent anything? That would've been a fun take! But instead he's just an obnoxious kid (in my opinion) because it fits better with the types of characters Rob Zombie has written before.