I found two aspects of the documentary notable.
A Universe from Nothing?
Krauss is known for his advocacy of the view the universe arose from literally nothing. Krauss says true nothing creates the perfect condition for something to pop into being, albeit with zero net energy (matter and antimatter making up part of the balance, for example).
The documentary showed Krauss appearing on the Colbert Report with host Stephen Colbert. Colbert, playing his usual role as the conservative rube, asks Krauss if there is no god in existence, if god is nothing, then therefore may we conclude that god created the universe? Laughter ensues, since of course that's a joke. But Colbert unwittingly has a point.
Critics have made a point of mocking the idea of God creating something from nothing. And now a scientist says its plausible from something to come into existence from nothing and we're supposed to take it as an evidence in favor of atheism.
The documentary doesn't deal with the anthropic principle. Dawkins badly misunderstands it. Doubtless Krauss would deal with the argument better than Dawkins, perhaps by invoking the multiverse concept. The problem, of course, is how one explains a universe of the type we have based on a random popping into existence. Some versions of the multiverse idea suggest an infinity of universes, making the one we know inevitable (along with all the possible universes). Do either Krauss or Dawkins contemplate the difficulties for that idea? Science Fiction writer Larry Niven wrestled with the idea decades ago, making a strong argument that it makes free will absurd. One literally must take every option and refuse no option. Walk off the cliff if you wish; another you will take the safer option. Or you can walk away from the cliff and leave the risk to your alternate selves. One of them will surely take the plunge if the infinity of universes is sufficiently well populated.
How About a Morality Based on Reason?
Dawkins spends some time advocating the idea that we can make our own morality, doubtless one that makes much more sense than those foisted on us by religionists.
But that's a problem right there. Atheists will tend not to agree on morality except where they agree the religionists are promoting something that's between 1 and 100 percent baloney. The view that morals are real (moral realism) isn't particularly popular among atheists. Morality exists only as normative patterns for those skeptics.
The morality problem shows up in the background when Dawkins and Krauss talk about how a democracy needs people who are informed so they can make intelligent decisions about stuff.
One wonders whether either atheist has anything more than a pragmatic appreciation for the democratic principle. Wouldn't both get on board with government by scientific elites? Who better to steer humanity toward a brave new world than those blessed with the intellectual ability to navigate a treacherous future?
"The Unbelievers" tries to paint a positive picture of unbelief, naturally, so the face of atheism in this film is intended to appear free of blemishes. That's unless we count the vulgar denouncement we see from atheists (?) confronting religious protesters.