Salary
Average Salary: $56,000
Expected Lifetime Earnings: $2,337,888
The days of Siskel and Ebert and Pauline Kael making a comfortable living from being film critics are buried along with them.
Most likely you won't make a dime.
Many of the magazines and newspapers that hired film critics have gone under. The few print publications that have movie reviews already have critics holding on to their positions for dear life and are counting the days until they're at the unemployment line.
Online sites usually go the free "community" route à la the Internet Movie Database, where anyone can post reviews on movies or TV shows for free and rate it by number. The numbers are averaged and that becomes what people want to see: numbers instead of words. This might not help you, the writer, but it certainly makes The Count very happy (zero, zero stars, ah ah ah).
Blogs are the thing, especially for movie buffs showing latent film critic tendencies. Blogs don't pay squat. Sure, there are those successful, Ain't It Cool News-y type sites, but those took years of painstaking building of an audience, and even then it started as a niche geek site (and still hasn't made its founder and über film nerd, Harry Knowles, a rich man).
You'll probably have to start one on your own and shell out the bucks for the website and hosting services.
If you're the one percent who actually talks someone into paying you to write film criticism, you won't make much. Maybe twenty-five to fifty bucks a review.
While your average film bloggist has to rely on a paltry $27,000 to get by, for those fortunate few professionals who have established themselves in the industry—and been given one of those top-level newspaper jobs—can make an average of $40,000-$60,000 annually, but good luck with that one (source).
The odds are better in Vegas. Oh well, you can always earn rent money by taking part in cutting-edge medical experiments.