E and Firemeboy both have valid positions and I think the truth lies somewhere in the middle.
A review should be able to describe a movie in such a way that the audience gets a feel for what the movie is like. In that way they get to judge for themselves. It's for this reason that "opinion" reviews are so vilified. If the reviewer only gives you his opinion without quantifying it with a why or a wherefore he's given you nothing... unless you know his tastes and can judge from there.
On the other hand, straight facts about a movie, whether it is about the military or the police or teenage girls, who performed in it, who directed it etc... is less than useful to the reader. He could get that stuff from IMDB and be none the wiser.
So the reviewer has to attempt to give an objective description of things like plot, character development and dialogue, all very subjective things. Often that delves into opinion.
I hated Narnia because they made the characters do stupid and unbelievable things to move the plot forward. That's a pet peeve of mine and I got crucified on the forums for having that pet peeve and daring to talk about it in a review. Yet at the same time, I voiced very clearly what I didn't like about the film and what I liked about it.
Everyone agrees with me on what I liked about the film, the CGI. But quite a few people don't agree on what makes good dialogue, believable character development, and steady plotting. Those are totally subjective but I was careful to detail exactly what I did and didn't like. Of course, I couched it in entertaining (to me at least) language but the facts were there.
So you have to walk the line. Give plenty of facts, make the review as objective as you can and be clear about WHY you liked or didn't like some aspect. But any reader also has to realize that he may not agree with what any particular reviewer considers good and bad and until he's read a couple of review by that guy, of movies he's also seen, he's not going to know for sure.