I've seen decent movies about a group of people locked in isolation for months on end -- this was not one of them.
I've seen decent TV series shows and movies where people thought they were in simulations, but weren't... and the reverse. This is not one of them.
The movie begins promisingly enough with good actors and a decent premise -- a mission to simulate manned space flight for 400 days. The "astronauts" climb into a bunker underground. They're told not to come out early or their commander will ensure their careers are over.
Long story short, they leave early - to find a desolate world inhabited by crazy people... or maybe they're aliens... or hallucinations. We don't know. I bet neither do the writers.