Interstellar is 2001 as remade by Frank Capra. That is to say, it's half hard sci-fi with a philosophical/mystical element and half sentimental family melodrama. Like many a dystopian story, not a lot of time is spent on explaining how we got where we are; suffice to say that at some point in the future, Earth is dying due to something called the Blight. Food stuffs no longer grow (corn is the last viable crop) and people are starving. The current generation sees themselves not as explorers or innovators but as caretakers of what few resources are left, to the point where children are being taught that the great breakthroughs of the past, like the Apollo moon landing, were faked so they don't dare dream of doing great things themselves.
At nearly three hours, this is both too long and too short. It's too long for one sitting—the plotline (story #2.75?) involving Matt Damon as an explorer from a previous mission felt especially extraneous even though Damon was very good. It's too short from the point of view of narrative. As I noted above, an entire movie could have been devoted to the backstory, so maybe this would have worked best as a TV miniseries. The screenplay was bloated with interesting ideas that never really got explained or worked out, and another couple of hours might have helped that.