The 400 pound gorilla in the room when watching "Another Earth" is that it is a low budget science fiction movie. You know that you aren't getting Star Wars, nor 2001 A Space Odyssey nor anything closely resembling those movies. This movie has far fewer special effects than the low budget "Monsters", but it is much more effective as a personal drama. As the trailer makes clear, this movie is about how people react to the impossible premise that a mirror Earth, identical to our Earth in almost every way, would suddenly appear in the sky. This is, of course, impossible, even if you talk about quantum physics and parallel dimensions, but the impossibility of the movie is not really important. This is a human drama about emotion, redemption, and second chances, all of which the movie does really well.
The movie starts somewhat predictably with a tragic car wreck that costs the life of a boy and his mother. The person at fault, Rhoda, finds her promising life ruined and she is wracked with guilt. She is very pensive. At one point she tries to kill herself. Things improve for her when she meets the widower of the family that died. His life is in shambles. He doesn't know who she is. She tries to introduce herself and apologize, but she loses her nerve and lies to him instead. Then she makes up an excuse that allows her to help him out, and gradually the two become friends. At some point she has to tell him the truth.
I expected a movie about another Earth in the sky to eventually show us what is on that other planet. Although the payoff is not what I hoped for, the ending is remarkably clever in the way that it lets us know what is on the other world. What happens next is left up to our imaginations, although maybe a more well funded movie could have explored this premise a little further.
The movie proceeds at a slightly slow pace, but I found it very compelling. It is very smart film that doesn't hit us over the head with a lot of explanation. The film is minimalist in every way, but it knows how to emotionally draw us into the story.