I say surprisingly because although anything that successful will usually attract some critics, KONY 12 is about the depredations of Joseph Kony, who for decades has forced boys into his military service in Uganda, forced girls to become prostitutes, and used kidnapping and murder to achieve his purposes. Certainly anything other than gratitude for bringing such atrocities to the world's attention is surprising.
Meenal Vamburkar has summarized some of the criticisms on Mediaite. They amount to "oversimplification" - a critique of the way the facts are presented in the documentary, and a claim that the 30-minute movie did not present all of the facts.
At least one critic has found fault with director Jason Russell's employment of his five-year-old son to carry some of the narrative. We see the boy, wide-eyed, learning and responding to what his father very carefully and tenderly tells him about Joseph Kony. If this was the sum total of the movie, then, yes, of course, this narrative would be an oversimplification, because you cannot tell a five-year all of those distressing facts. But Jason's son is just a part of this movie, and in this role I thought his screen time was one of the most effective presentations I've ever seen in a documentary (it was reminiscent of the excellent documentary, Tiffany Shlain's Connected, about human connectivity, released last year). All of us who didn't know about Kony before this movie are in effect in the same place as Jason's son.
As for KONY 12 not including important information, I would say it's ipso facto impossible for any 30-minute documentary to provide all significant information and details on any subject, even if everyone agreed on just what those details were. So does this mean that no one should make a 30-minute documentary on an important topic? Of course not, and the public's remedy for any missing information is to provide it.
Which gets us to what the movie wants to do, and wants us to do. That would be, first and foremost, to learn about Joseph Kony. The movie explicitly invokes Facebook and social media, and asks viewers to talk about Joseph Kony to the world audience that social media (or, what I call New New Media) have engendered. The movie's critics are doing just what the movie wants, and if the heightened Kony profile leads to an end of his horrendous activities, that would be a great victory indeed for social media and the people of the world.