Why the dreamy "aberrated" ending

Rating: 6/10 (11 September 2015)

Interstellar as a movie wasn't bad at all. My only problem with the movie was how the story conveyed the perspective of the gloominess and the extended boring and silent moments that made it less interesting.
Another problem was the ending, it was totally unexplainable and lame. So "why" do such a great movie, then ruin it with such unnecessary strange anonymous ending with Anne Hathaway living alone in a seemingly depressed way, while Matthew Mcconaughey is living in another spiral world and all of a sudden: The End?! Unless there's a sequel, thats unacceptable.
I know that some may enjoy the visuals and the idea of the after world, but thats simply letting the viewer feel in some way empty and kind of regret watching a movie that may be overrated "a bit" due to the scenes I have mentioned before.