As someone who has recently been re watching early Naruto. It's very easy to see why she is so disliked. She constantly berates and hits Naruto, with having no accomplishments or contributions to speak of. Her fight with Zaku in the FoD is kinda pathetic, the fucking bites his arm. Her fight with Ino in the Prelims is built on a vain rivaly over a boy, which they threw away a friendship over. Also all the stuff that happens in Shipuuden just makes it worse.
I suppose I'll be the one to defend Hinata. She's cute as hell, is a girl that's not screaming about Sasuke, and has reason's to define her crush on Naruto. She works hard, just as Naruto and Lee do ,but her attitude of self-depreciation holds her back. Her backstory is interesting, as is her relationship with Neji. She almost gets herself killed in her fight with him. Also before the Chunin Exam finals, she emotionally supports Naruto when he opens up to her about his uncertainty with his upcoming match. There is definitely stuff I'm missing but that what I'll put out there. Also you guys spouting that bland shit sound mad salty.
Another point. I hated Sakura way more in the past, and that was probably because of the anime, it can exaggerate and stereotype some of the traites of the characters, like Sakura's anger and Hinata fainting and stuttering.