Biosphere takes a wonderfully strange premise and builds an intimate science-fiction story around just two people. Sterling K. Brown and Mark Duplass have excellent chemistry as the last two men on Earth, and their friendship gives the film a surprisingly warm center.
What starts as a post-apocalyptic survival story gradually becomes something much stranger, exploring masculinity, identity, adaptation, and what humanity might require to survive. The limited setting works in the film's favor, keeping the attention on the performances and increasingly complicated relationship between the characters.
I especially liked how willing the movie is to follow its central idea into unexpected territory without losing its sense of humor. It's funny, awkward, thoughtful, and occasionally bizarre.
Overall, Biosphere is an inventive little sci-fi film that proves you don't need a huge budget or elaborate effects to explore a genuinely big idea.