Roger Ebert is known for being somewhat of a pushover when it comes to doling out star ratings on his reviews (according to metacritic.com, he grades movies 8.9 points higher than other critics on average). Ebert defends himself in this essay by saying he likes movies too much, he has sympathy for genres and that he feels strongly about actors he admires.
Ultimately, though, Ebert is backed into the same corner every critic is backed into when having to defend their star ratings and not their reviews. ("If you disagree with how many stars I gave it," he writes, "you can mail your opinion to where the sun don't shine.")
This is generally why most critics despise the star rating system: It's the number of stars, generally, that readers obsess over the most. And although I know a four-star or one-star movie when I see one, most films aren't quite that cut-and-dried.
Take Righteous Kill, for example. I was certain I was going to give it a single star when I sat down to write my review - it's pretty awful - but by the time I had finished, the rating had mysteriously gone up to two stars. Why? Because I realized that as bad as the movie is, I had enjoyed watching De Niro and Pacino too much to write the film off altogether.
For the record, according to metacritic, I rate films .8 points lower than other critics on average. I'm a hardass. My colleague Connie Ogle rates films .1 points higher than other critics. Especially if they happen to star David Duchovny.