Roger Ebert says it better than most (as usual):

"The Dictator" is funny, in addition to being obscene, disgusting, scatological, vulgar, crude and so on. Having seen Sacha Baron Cohen promoting it on countless talk shows, I feared the movie would feel like deja vu. But no. He establishes a claim to be the best comic filmmaker now working. And in a speech about dictatorships, he practices merciless political satire.

...

Although the movie very casually follows the progress of the romance and the assassination scheme, Cohen and the director, Larry Charles, are about as dedicated to plot as the Marx Brothers; the movie's spiritual ancestor is "Duck Soup" and Groucho's Freedonian dictator Rufus T. Firefly. There is also a taste of Buster Keaton's physical humor in a scene where Aladeen attempts to slide on a cable high above the street into the upper floor of a hotel.