Normally I would be able to predict the ending which though it doesn't make the show any less in my opinion, it can get a little boring now and again. So being surprised was a twist in of itself. That Castle would set up the fund clearly shows his feelings for Beckett, though for a moment I was worried she would have a go at him for interfering – again! A good use for the profits from the Nikki Heat novels, and a nice way to pay back Beckett for having to deal with Castle every day.
And the show did explore the various aspects of what others might do with a big win, it does make one wonder, and it also shows the downsides. The guilt and changes it makes to a person's personality.