See? It can be done.

"Iron Man" shows that a movie based on a comic book can have thoroughly developed characters, a compelling plot and a sense of humor.

The early "Superman" movie and the first couple of "Batman" films did it too, but it's been awhile.

"Iron Man" stands out because it has the trifecta of effective filmmaking: a clever, character-based script, surehanded direction and an outstanding performance by the lead actor.

Robert Downey Jr.'s long and not undistinguished career has been leading to this point; it is as if every role he has played has been a warm-up for playing Tony Stark, billionaire industrialist, man about town, drunk. As Tony, Downey plays to his strengths. He is boyishly charming, roguishly irresponsible, quick-witted and appealingly dissipated.

Downey has been served a fastball down the middle, and he knocks it out of the park. But much of the credit goes to the four writers, who have created such a delectable character. Along with granting him with a flashy lifestyle and cheeky attitude, they have thoroughly thought him through to give him a business philosophy.

But best of all, they give him a genuinely funny sense of humor, loading him up with sometimes hilarious witticisms and throwaway lines that Downey then tosses off with a brilliant nonchalance.

There are stretches in the story when Tony has to be serious and not make any quips. The film is the poorer for these periods.

Tony is a famous and successful head of an armaments company, doing his part to keep America strong and the rest of the world safe. But while demonstrating weapons to Army brass in Afghanistan (why Afghanistan? Um . . . why not?), he is attacked and held captive by terrorists armed with his own weapons.

They want him to build them a weapon, but he uses the materials instead to construct a heavily fortified and invulnerable metal body suit -- that can fly.

To be honest, the film gets a little fetishistic about this and a couple of subsequent suits. Too much time is devoted to their construction and the process of wearing them, which may satisfy the obsessive fanboys but it slows down the story's pace.

The film recovers and all goes relatively smoothly until the ending. Perhaps the rest of the movie builds up our expectations, but the climax is unoriginal and disappointing. It will have you sitting at the back of your seat.

Director Jon Favreau, who appears in the film as a chauffeur, is strong in the character scenes. Despite the weak climax, he keeps things moving (most of the time) at a decent, but unhurried, clip. Former Richmonder Leslie Bibb is also in the picture in a small role as a magazine reporter, which leads to the funniest line in the movie. Whoever wrote that line should get an Oscar for that joke alone.

Although it is uneven at times, "Iron Man" is at least a good half-ton of fun. Let's hope they don't ruin it with a sequel.