I just saw a post on The Endeavor about the solution of the Collatz conjecture. Here is the paper which claims to prove the conjecture. I can't understand it.
My first reaction was disappointment. I think because I always felt capable of enjoying the problem, yet it's pretty clear at a glance that I am not capable of understanding the proof. It was a very accessible unsolved problem, but as a proven statement, I suppose its simplicity will make it less interesting, reduced to a bit of trivia and not the sort of treasure hunt that fills up pages of my paper.
My second reaction is that Gerhard Opfer must have really enjoyed proving this, and I envy him that thrill. I've only ever proven things that other people already knew.