My philosophies on rating are fairly simple- People naturally create frameworks when engaging in creative pieces and our standards aren't drastically different from one another making artistic merit (more) objectively traceable. At any rate, I feel this is better than throwing around obnoxiously relativistic blanket statements about subjectivity and disregarding the value of thought out analysis. Ultimately true merit comes from a broad understanding of what is in question and how well one can articulate their points about it.
That being said I like to think I put a lot of effort and thought into my ratings. I take a lot things into consideration and strive for consistency. I don't rate entirely on "enjoyment" so a low rating doesn't necessarily mean I dislike something. As far as going from genre to genre, I know not every work aims to change or challenge the medium, but the highest praise should certainly go to the ones that do.