This is something that I realized over the last week, since I had just purchased Mr. Jack, and played it. And found it to be the game that I wished I had designed. Mostly because I feels so unique to almost everything else I have played.
Things of note:
The game has a very chess-like appeal to me (with the constant "look ahead" of moves) without being anything like chess.
It feels very themed (due to the nature of the character special powers and the way they interact with the game environment).
It has a very unique approach (to my knowledge) of how to "solve" a deduction game, without resorting to the usual Clue-based tropes of "do you have this card in your hand".
And so, I'm interested in hearing what other people would have to say, with regards to games they wished that they have designed. And no, "because it's popular and I'd be extremely wealthy," is not an answer.
Interestingly enough, I happen to have a working Dark Tower.