Every reviewer uses some basic formula to show pleasure or pain after viewing a film. These range from "good and bad" to "thumbs up or down" to various numeric systems. On this site we'll be using a simple 1-6 star formula that is straightforward while also allowing for a bit of nuance.

1 star: Atrocious.
2 stars: Bad; some redeeming value.
3 stars: Mediocre; nevertheless, it has its good points.
4 stars: Very good, but either it's limited in some sense or I have real reservations regarding basics like plot and/or acting.
5 stars: Excellent and probably very original. It could be brilliant-but-flawed, or just so good that one can't demote it further despite moderately important flaws. Brings me out of myself.
6 stars: Superb, knocks me out of my socks. It transcends any faults, such that one simply ignores or doesn't notice weaknesses that might occur to one later, even obvious ones. More than survives and is very often better with a second viewing (this also applies to a 5, of course). Great originality is a given, and it's likely that the acting is near perfect.

Major considerations: overall impact in a non-analytical sense, acting, plot, cinematography, music. Movies often get a disproportional plus/minus for having a single outstanding or pathetic quality in one area, e.g., originality (versus predictability); beautiful and/or brilliant cinematography (versus plain or 'pretty' cinematography); humor (versus sad, cliché-ridden attempts at humor); profundity (versus banality or bathos); and just being a lot of fun instead of the usual boring fare.