I really liked the movie overall, and i'm usually not very fond of Nolan... Well I think Nolan is probably the best currently you can get behind hollywood blockbusters, and by far, but I did not really like Batman for example, and loathed half of Inception.
So, I think what Interstellar nailed right is most of all, the atmosphere, it's gloom, dark, and I felt rather oppressed from the beginning to the end. Even Zimmer did a good job instead of his usual vuvuzela harmonics. Not saying it's an original score worth of praises and accolades, but it actually fits and enforces the atmosphere and the oppression. The whole movie probably itself gets its inspiration in 2001.
It also touches many interesting scientific subjects, and the gripe I have is that it does not really get into details about them, just leaving references, but references about things that the audience MUST understand to follow the movie. It's half between hard science and fantasy, and it doesn't focus on explaining. I could understand it if it was a total hard science movie, but here it's definitely not. I know many people that are not into science and SciFi like I am that didn't understand much of the movie to actually appreciate it. They already had a hard time grasping the concept of time relativity, which is probably the only scientific concept that is scratched enough to be explained at least a little.
But when they start to talk about 4th or 5th dimensions and tesseracts, just mentioning it like that once, well you bet that most people were like "wtfisthis?"
Also, like Silas, some weird irrational stuff, for sure, but the thing that irritated me to no end was their plan to drop the robot inside the black hole event horizon, playing on some kind of speed effect or some nonsense to hope see it get out just after ? Lol wtf ? Isn't the very definition of an event horizon that NOTHING gets back past that point ?
So, all in all, I do think that unlike 2001 (which is a masterpiece hard to approach, true), the movie more or less fails to tackle a clear and interesting theme and message, except maybe the sense of impending doom/apocalypse that takes you to the guts from the beginning to the end, doesn't raise a lot of questioning, but artistically however, it's great. Overall, I think it is a very good movie.