My answers to both these questions are the same, since I would always want to author a game I would also want to play. Here's three off the top of my head, I will post again if I think of more.
(1) 1893: A World's Fair Mystery
I just finished this game and the setting was amazing, especially with QTads providing the pictures, the compass, and the music. It was a fantastic simulation. I would like to see a less puzzly and more mystery-oriented crime story of H.H. Holmes as a sequel.
(2) Lost Pig
Grunk is a self-contained, entertaining, funny, and highly stylized PC that could work in pretty much any context for a sequel.
(3) An Act of Murder
One of the few mystery parser games that actually works and is replayable. I think there is potential to make this genre really work without railroading the PC and without missing critical information at certain times in the simulated world of NPCs.