Last week, a reader emailed me to ask about star ratings -- he was curious about criteria for the middle ratings, whether I ever gave a movie zero stars, and if I would give examples for each rating. Glad to oblige! I'll admit I'm not crazy about giving star ratings, but appreciate that they are customary. It's frustrating, though, that a two-and-a-half star rating can mean a movie that's kind of OK but utterly unambitious, or a movie that's both amazing and terrible at the same time. And I also recognize that star ratings are entirely subjective; a four-star experience for me might not be the same for you, and vice versa. For me, a three-star movie isn't necessarily "better" than a two-and-a-half star movie; but it did a better job of doing what it sets out to do -- in other words, I'm rating the movie not against other movies, but against itself. Does that make sense? Anyway, here are the eight possible ratings, with a few thoughts:

Four stars: A truly wonderful movie; a transporting experience; something for which I can't imagine how it could be any better. Recent examples: "The Artist," "The Descendants," "Pina" (which I just wrote up today).

Three and a half stars: Very, very good; among my favorites of the year; maybe just one little thing about it that feels like a misstep, or perhaps overall it's just not quite as overwhelming an experience as a four-star movie, but still a genuine pleasure. Recent examples: "Margaret" (just shy of four stars, as I felt a few of the characters were undeveloped; perhaps due to the movie's well-publicized recutting); "Pariah," "The Girl with the Dragon Tattoo."

Three stars: Good, solid movie; recommended; no major qualms. Recent examples: "Albert Nobbs," "The Woman in Black," "Young Adult."

Two and a half stars. Now we're getting a little murky. This might be a movie that's solidly mediocre, or a wildly ambitious movie that only partially fulfills its ambition, or a movie that's got some great qualities or uneven execution. Recent examples: "The Innkeepers"; "War Horse" (yes, I know nobody agrees with me on this); "Sherlock Holmes: A Game of Shadows".

Two stars: Not recommended; needs a lot of popcorn; not good but there's something about it that keeps it from being truly bad -- maybe a strong performance or impressive effects. Recent examples: "Carnage," "W.E.", "Chronicle," "The Iron Lady."

One and a half stars. Now we're getting into the dreck. Not good; not worth your time; maybe not offensively bad but bad all the same. Examples: "The Hangover, Part II."

One star: Bad movie; indifferently made and maybe even a little insulting and/or offensive in its use of our time. Examples: "30 Minutes or Less."

Half a star: Really, really, really awful. Examples: Can't think of any; I know I've awarded half a star in the past, but it's been a while. (In general, I'm noticing as I look back on these ratings that I tend to err on the generous side. I'll work on that.)

No stars: Haven't given this as a rating, as I think it would just look as if I'd forgotten to rate the movie. But maybe I should.

And what about you -- do you find star ratings helpful?