I've been having some struggles here lately in dealing with different genres and keeping a consistent rating process throughout.
One of the easiest ways for me to evaluate what I read has always been through a straight-forward process. Thus, my review format makes it easiest for me all around to come up with a rating that I feel is most representative, and it gives me an idea (currently and in the future) of which aspects of the novel I liked and which I didn't. Sometimes I won't even know what I think about a book when I finish until I take the time to pick it apart and just start writing or talking to someone, and as I'm doing that then somewhere along the way my opinions just roar right into view and suddenly I know exactly how I felt about that book.
I usually don't have any problems with this way of reviewing books. If a couple things end up off at the end, I usually just re-evaluate my subcategories and adjust accordingly. Sometimes I'll "curve" a review one way or the other. For instance, a book might score just "ok" in all categories but for some reason I'll have ended up liking more than the final score represents. It might be the overall feeling of the book or a level of excitement or enthusiasm that certain parts didn't catch. But this is few and far between and usually only a few decimal points raised or lowered.
But I've been finding lately that I'm struggling with the rating between, say, a fantasy novel and a realistic/contemporary romance novel. For characters and writing style, sure, the rating is relatively consistent. But what about plot? How do you rate something on plot? I've noticed myself writing in some of the romance novels "Not much happened by means of plot", but what do I mean by that?
I think I mean that the conflict in realistic novels is often more internal or character driven than external. So what does that mean for plot? It doesn't mean that nothing happens, just that it happens differently than a paranormal or fantasy novel. Does a realistic fiction deserve a lower plot score than a fantasy or epic novel simply because there aren't as many twists and plot devices and "stuff"? It definitely shouldn't. That doesn't mean that it doesn't end up happening.
In general, I like both genres, I just think that each needs to be judged on its peers and with its own expectations. A realistic novel isn't going to have as much "stuff" happen necessarily as a plot-driven fantasy novel, but that doesn't mean that I don't enjoy it.
So, the brainstorming keeps on with this one. Will I have to adjust my rating scale someday? Maybe, but for now I'll just keep in mind that each genre is different and I need to be judging the books based on themselves, not something entirely different.