Film being an extremely subjective experience, rating a movie might seem arbitrary and pointless. One man's trash is another's treasure, so how can you even compare? The only way to give someone an idea of how good your cinematic experience measured up is to rate it on some sort of scale. But which scale? Every reviewer has their own rating scale, and each has it's strengths and weaknesses. Do you use the binary scale of thumbs up vs. thumbs down? Roger Ebert's 4-star system? The pointlessly precise 1-100 scale?
CineRater uses a simple 5-star rating system, with a couple rules:
1. No fractional stars. I prefer rating like this because it gets to the heart of how you really feel about the movie. It forces you to make a tough decision; no fence-sitting. The closest I'll allow to cheating this rule is indicating that a movie achieved a certain star rating, but just barely (saying, "this movie gets 3 stars, but just barely escaped getting 2" instead of "2.5" or "if it had better acting it would have been a 4, but sadly, I have to give it a 3" instead of "3.5").
2. Movies are rated in a vacuum. That is, movies are rated on their own merits, not based on if another movie did the same thing better or worse. Each film is treated as a self-contained piece. Perhaps a movie is derivative and borrows plot elements from things that came before, and that will be reflected in the actual text of the review, but when it comes to star ratings, I'm more interested in two questions: "Was the movie enjoyable?" and "Did the movie achieve what it was attempting to do artistically?" Both of these things taken into account, and processed through my subjective tastes and interests will constitute the final star rating.
Here's what each star rating ultimately boils down to:
A 1-star review is the absolute floor of the rating system. This is a movie that was agony to watch. A movie that didn't deliver on what it promised on any level. Something you never want to see again.
A 2-star movie is one that did some things right, but overall is mediocre at best. You probably wouldn't recommend it to anyone, but you didn't absolutely despise it.
3 stars indicate that a movie is enjoyable. You liked the movie, and you might even recommend it to people. It has its flaws, and it isn't quite "high art", but it does its job, and you wouldn't be against seeing it again.
A 4-star movie is something you really enjoyed. You'd definitely recommend it to friends, and you were excited and engrossed by the experience of watching it.
This is a movie that is quite possibly perfect. It blew your mind and, given a decade or two, might be considered a classic. You would recommend it to anyone and consider it your duty as a human being to sing its praises to all within the sound of your voice.