What science fiction does best—and I mean real, aliens-and-alternate-timelines, spaceship-y sorts of science fiction here—is unsettle us, the viewers. Not because of how terrifying everything is (although let's never forget that moment of abject horror in Alien when the alien bursts out of Kane's chest and leaves everyone screaming): that kind of unsettledness is a given.
No: When science fiction is doing its job, it leaves us feeling uneasy not about the world it creates, but about our own world—and ourselves. Sci-fi is by nature about what could be, about things that might plausibly happen, given a little bit of time and maybe a wrong turn or two in the lab. It looks at the consequences of scientific innovations, and it makes us ask basic questions about identity, institutions, societal structures, desire, morality, and ethics.
From Star Trek to Alien to 2001: A Space Odyssey and WALL-E, science fiction always works best by taking the familiar (people, places, relationships) and putting it in the unfamiliar (outer space, other planets, the future). Thus defamiliarized, we silence our reflexive reactions to ethical dilemmas and prejudices just long enough to let them sneak past our defenses like (forgive me) so many shape-shifters and make us realize that we're empathizing with a morally reprehensible action or character.
So the only real problem with Oblivion—which is a perfectly adequate, shiny Tom Cruise-driven futuristic action flick—is that it never asks us to be unsettled. In fact, it seems calculated to make us feel comfortable. How much you care about that may be worth considering. ...