I get the impression--but then, I'm still a newbie here--that the general distaste held for RD's characters has as much (or more) to do with offscreen things than onscreen. Particularly his demeaner at one or two specific conventions, and the fact that other castmembers have broadly hinted at friction on the set.
Try as I might, I can't see anything in the show itself that would lead people to think of him as annoying--his quirks are no weirder than those of the rest of the cast... Almost everyone has some silly habit or another. As a whole, I find them endearing.
Not to say that I'm any special fan. (I chose the name CD Tate here thinking it would be a reasonably obscure reference, not realizing that it would brand me for life in the forum. Let's just say I'll be glad when he's gone too, so I won't need to keep hearing the tirades every day...)
People like to jump on bandwagons, and people like to make fun. Nothing wrong with that... But as someone whose only contact with Dark Shadows is the show itself, I can't figure out why all the animosity. Other than to humor our Mysterious Benefactor, that is...