The guy who does cinema sins is actually very knowledgable about films. Some of his stuff is random nitpicks for the laughs, but other times his nitpicks about the plot, characters, in movies is spot on or things you just over look. Honest trailer is good but in my personal opinion I find cinema sins to be more in depth and funnier.
I think people dislike cinema sins because they rip on all movies even popular ones, so maybe they made some fans mad. I remember when Nolan fanboys got butt hurt about the Honest Trailer dark knight rises video. They all said honest trailers was stupid etc. So I guess the same is true with cinema sins.