In regards to why I like LSH, it's probably best to say that I like "terrifying" as well as shock. Her introduction in the epilogue of SoS, was absolutely that. One of those moments where I could actually hear/feel my jaw hit the floor, and just sat there gaping trying my best to think/visually imagine what the hell just happened. the image of a grotesque, disfigured, gaping slit in neck, Cat with those frecking HATEFUL eyes...man, absolute ****ing chills. THAT is **** that makes me enjoy reading/film. Such an incredible feeling for someone whole loves horror, tension, and supernatural. You talk about Cat being the most annoying character (which isn't quite true, though I'd agree she's top 5 in the category), well Stoneheart isn't ****ing Cat. I'll gladly take this monstrosity of death and cold vengeance over reg Cat or some of those other annoying characters.
I think you make a good point about GRRM's inability to let concluded plot lines rest and how part of that is why he's struggling to finish this series. Of course, you have to remember LSH is only the 2nd (1stish to a degree; we see Beric do it before, but then again he actually dies for good before we see LSH) character to actually come back from the dead. So if you're going to complain that she cheapens death and be a prime example of Martin struggling to finish his books, you better complain about Jon when he comes back (not to mention the others that have/may come back). I think there are much worse things/storylines/characters than LSH that are taking a toll on GRRM's writing.
and cheapen death? ****ing tons of people have been killed and have not/will not ever come back. in the show though, I guess you are correct/have a point only because LSH would be like the 3rd person brought back from the dead in like 5 episodes. that does annoy me a bit honestly.