I agreed with Goober, so I won't repeat his list, but I'll add mine...
The video spends too much time on a particular area of her body, or she shows too much of it, and not enough of another.
Anal sex. Sorry, I know some are fans, but I find it revolting.
Girls seemingly indifferent to sex. The first time I saw Alexis Texas hardcore (I'm a mild fan), she was encouraging her partner in a tone similar to advising what groceries to buy, while he seemed to be having a good time just pounding the hell out of her.
Girls that sound fake in moaning. Laura Orsolya & Maggie Green are hot to look at, but that Michigan-style accent is a total turnoff. They sound similar to geese honking.