As I said to Aiko before, ratings are more of a personal thing than anything serious. I mean, it's obvious there's not one grand metric for rating: it differs between people. Most things I rate highly are because I find the themes to have some relevance to my life or it was just that enjoyable. I'm (mostly) not doing it out of spite, it's just what I like and what I don't like.
For Death Note I stopped after that guy went away, it was on my stagnant watching list for a long time. I knew what was going to happen so I never felt the need to continue.
For SAC, I think it's the lengthy dialogues which badly needed terseness and restraint; I'm not much of a fan of action, either. Don't get me wrong, there was an element of enjoyment there: I liked some individual episodes, I'm receptive to the setting (the movie is great), and it did make me read The Catcher in the Rye; but, all in all, I don't hold it in esteem.
I don't hate them (some I do, however), so I wouldn't hesitate to recommend them to others.