I have to say, I had one reviewer elsewhere who did the good, the bad and the ugly when he reviewed. He was harsh, exacting, and almost universally hated, and the first time he left me a review I read it twice, re-read my chapter and PM'd him to discuss some of what he'd said because it was utterly valid.
I wound up actually enjoying verbally fencing with him, and while there were times I disagreed with his critiques as being purely opinion and therefore inherently a matter of personal bias, he made me think and grow as a writer. He could have been nicer, and he wasn't nearly as good a writer as he was a reviewer, but there was gold in his criticism.
So, if I got a review like the one above, I'd re-read my chapter or story, and try to see it from the perspective of the reviewer. Even if I didn't agree fully, I can almost bet there'd be something in that review that would help me improve. Then again, I'm serious about writing, and I'm serious about improving my writing.
But the idea of sandwiching concrit between layers of positive comments is a good one as a general rule of thumb. People are always more receptive if they don't feel defensive, and criticism tends to make us defensive, doesn't it?