the ending

Yes. The end twist was that Darris Cain was, unknowingly, in a video game. The inmate kept telling him he'd been there before because he had- every time the player played that level. To clarify the twist, the screenwriter added a little flashback at the end to kind of say, "See! There were easter eggs in the movie the whole time, you just never figured it out!" It is also understandably a videogame because the player had no previous records, yet he kept coming back up in the same place,unwittingly. Think about it. Everytime you restart a game, you appear in the same place over and over again, but the stuff you did in the previous game has no bearing on what you're doing now.

Hope that cleared some stuff up. Great movie, BTW.

*SPOLIER*

Yep.

To add to that, video game enemies or their AI only have one sole purpose in life - to kill the player.

Watch it again, Agent Cain said something about the purpose of his life near the ending.