how come so many people have been hating on henry?

Myself I never hated on him. :) My brother finds him annoying because he keeps saying "it's the curse" in the first season and similar things xD I find this more funny since he's the only one who knows everything apart from Regina and no one wants to believe him and that's why he sounds like a crazy kid. Second season I was kind of disappointed that he didn't show a bit more support for Regina's redemption. I'm not saying he didn't support her or approve of her redemption just saying that he could do a bit more about incouraging her. Though him and Emma were the only ones showing any support for her. Other than that I quite LOVE that kid=) He has his moments. And sorry about my English. I'm still in the learning process. xD

I'm annoyed by his treatment of Gin a yes, but I don't hate him.

I nearly always don't like child characters in TV Shows as I find them unrealistic, often precocious, and generally annoying. Henry isn't as bad as he could be, I'm indifferent to him but certainly want him to be rescued. At the same time I do give him a lot of leeway when it comes to his actions, especially regarding Regina, because, you know, he's ten.