I don't hate Riley, exactly. I think it was important for him to be in the show, with Buffy, even for just a little while. Having the comparison between him and Angel was a good thing, and it was also when Buffy, and I think it was also the reason Buffy discovered she preferred evil men; and the others realised she seemed to like it when men hurt her, because she'd been with a normal man, and she hadn't been happy.
Riley was quite annoying, and he did tend to be quite boring and overly jealous (Especially about the Dracula situation) but I didn't hate him; I've not hated a Buffy character, ever, really.