Imagine a community where everyone is your clone, you exact copy with your same memories. But you don't notice it. Also, imagine you are fighting enemies which you believe are aliens from outer space, while they are humans. But you don't notice it.
If you can believe all that, you are welcome to Oblivion, a Sci Fi blockbuster featuring big Hollywood stars, great visuals and an intricate plot about humanity VS. aliens, maybe, but you are not told which is which. Not the best movie Tom Cruise starred in, yet not bad if you like the genre.
