I think everyone has their own rubric for reviewing (at least they should, even if they're not aware of it.) Whether you decide to base that off of difficulty, fun factor, accessibility to all level of players, good chi flow, whatever, the most important thing is to stay consistent from review to review.
My personal rubric checks the amenities, use of available elevation, water, and other natural land features, variety of hole types, and good opportunities for risk/reward. But the number one most important thing for me is fun factor. Some courses just have a certain "feel" that exudes fun or detracts from it.
Also: changing ratings seems reasonable in most cases. I've rearranged my ratings several times as I've gotten more courses under the belt. It's ridiculous to realize you made a mistake and not change it to reflect new wisdom/knowledge.
I have a personal rubric also, but there is NEVER a scenerio where I will change a course from a 3 to a 5 without making a single change to the review.