The Moving Arts uses, essentially, the industry standard when it comes to giving films some sort of rating or grade.  The basic 5-star scale:

★★★★★ = Magnificent achievement in the arts.  A transcendent masterwork

★★★★ = Excellent film.  A “must see.”  Good enough to own

★★★ = Fairly entertaining.  Good for a matinée or a rental

★★ = Comparable to watching your cat chase around the laser pointer

★ = As good as food poisoning, stubbing your toe, or a terminal disease