I was really expecting some kind of twist and when one didn't come I was really disappointed. Hey, your robot is on the fritz. Want us to check it out?
NOPE.
I've complained about it before and I 100% don't think it was intentional but the character of his son is just completely and utterly forgotten about after the film portrays him in a bad light as an adult when was basically given no agency in his own life so his sister could pursue space magic. There's a small number of viewers that cannot see Interstellar as anything other than "Hey Dad, Remember Me? - The Movie".
I believe it was fixed in the novelization.
I think that what happened to his son (Tom) was probably lazy writing. But I think the fact is Tom and Murphy were just two completely different characters. Murphy was the sharp genius kid that was destined to do great things, and Tom was the boring farmer who had no hope of a substantial future. From the beginning of the movie it's clear that Cooper has a different relationship with each kid. He barely even talks to Tom about leaving forever, and the grandfather says "oh Tom will be fine" but they both know Murphy will be destroyed by it. There's a few interesting things I've always enjoyed about Tom and CASE. Cooper uses the line "take it easy turbo" to both Tom and CASE in the movie. Tom wears a hat with CASE on it (see above), and Case is a brand of farm equipment. And Case kind of has the boring functional personality that Tom had. So I've always felt that Cooper saw his son in CASE. Even though Murphy ended up saving the human race, CASE was able to save both Brand and Cooper during different parts of the mission. TARS (an anagram for star) was a much more vibrant robot full of personality. I felt Cooper saw his daughter in that robot. Mann's robot was "KIPP", which is an obvious homage to Kipp Thorne.
I think Mann's attempt to kill Cooper is a little stupid, but I can understand why Mann lied about his data and turned on the "I'm alive" signal. There's an overarching theme of love in the movie, so it makes sense that Mann did not like being alone and needed humans to come out to him. I mean he could have said "thank you for coming, this planet sucks, lets go somewhere else." I'm sure there's something about how they kept saying Mann is "the best of us" and even with that he can still be a coward, selfish, and a murderer. And of course Mann is the best of Man(n) kind.
No one has written in the last few pages about the "love" speech that Brand gives. I always felt that applied because despite everything, Cooper loved his daughter, and she loved him, and he knew that she would still have the watch and be able to receive the data through it.
I also have wondered what percent of people that don't like the movie are without kids. The emotional impact of the movie, specifically the entire leaving his daughter sequence, and then when she pops up as an adult on the recorded message screen, and then when she sends the message accusing him of leaivng her on earth to die (something that affects him so much he is willing to risk ending the human race to go comfort her) destroy me.
For me, this movie hits all the notes. Devastating familial consequences, space travel, beautiful scenery, interesting and accurate physics without an overly complicated plot (Tenet), and a perfect score.