
In a nutshell, Elysium is an ark ship, carrying 60,000 people and the stuff to colonize the first habitable planet found by Earth. But soon after leaving, the crew learns that Earth and all its civilization is gone. Ben Foster (3:10 to Yuma) and Dennis Quaid wake up from prolonged cryosleep not remembering who they are or what's going on (apparently a side effect of prolonged cryosleep), especially since the 4th flight crew (they are the 5th) did not wake them.
The title, Pandorum, is their word for space dementia. Beyond the SF, it's also a haunted house flick with action and psychological drama tossed in.
There are a couple of very good twists toward the end, one which could be guessed (I did, but I was spoiled). The problem I had with it was some of the angles and the darkness didn't let me see what was really happening all the time. Of course, the ship is suppose to be dark, so maybe I'm just nitpicking. A second viewing cured the problems, and it is, IMO, imminently rewatchable.
There's also good director's commentary for those who like that stuff.