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.  Will show up on many “Greatest” lists

★★★★ = Excellent film.  A “must see.”  Good enough to own and watch on a regular basis

★★★ = Fairly entertaining.  Has its highs and lows.  $1 theater or rental.

★★ = Less entertaining than watching your cat chase around the laser pointer

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