The last 30 minutes I assume you mean the scene inside the black hole? Where he tried to explain every little detail of what was happening? That was "show don't tell"?
I'm curious to hear particular examples where he violated the "show don't tell" rule. Scenes that you think would be better served with no additional explanation (assuming that is what you mean). Especially during the second part of the movie.
I agree that they hammered home what was happening a lot, but it was during a set of scenes that tied the entire film together, so the exposition can be forgiven.
The "show don't tell" violations that really stood out as being particularly awful were the banal ones. For instance: "How do we get the viewer to understand that the world has changed?"
*"You're telling me the textbooks say the Apollo mission was faked?!" said the character who was supposedly a pilot for NASA? He seriously didn't know that that had become the dominant view?
*Probably like 3-4 different lines about how we need farmers, not engineers, because, y'know, dust. Because the giant dust storms didn't explain it enough
*Instead of having her act quirky or demonstrate an interest in astronomy or science, the parent-teacher conference and repeated dialogue lines explain how Murphy has a great scientific mind
*Why the fuck would Anne Hathaway be explaining a black hole/worm hole to Matthew McConaughey's character 5 minutes before they were about to go into one? He didn't know?
*Anne Hathaway's terrible, emotionally stilted, weird speech about love in response to the "which planet should we go to" question, completely out of nowhere, about a character we've never met and who is dead, per the post above
*Matt Damon's "KIDS ARE IMPORTANT" speech to drive home the point over and over and over again about family/love/human relationships instead of having character development and believable interactions on-screen
I could go on, but you get the idea. I really wanted to enjoy this movie, even though I don't like Nolan films, but he has a seemingly complete inability to write good dialogue and coherent, believable-even-in-the-movie-universe plots, and to convey any emotional depth whatsoever. What did we really learn about McConaughey's character, or Hathaway's? Basically nothing. They're just plot devices to move the film on to the next visually impressive sequence.