Short Version: The most sparse game so far.
Number of Lighthouses I have Taken Lightly: 1
"The Lighthouse" by Eric Hickman and Nathan Chung is so sparsely implemented that it almost does not exist. Not that I think a count of locations and objects actually lends to aesthetic legitimacy or implies depth in IF, but:
Objects (counting doors): 12
With that in mind, the introductions begins
"You walk up to the lighthouse. It's large wooden frame creaking in the wind. You then step in front of the door and knock. Silence. Then the door opens and reveals the face of Mr Webster."
I've been seeing this sort of thing a lot. Bearing in mind that I have not written any IF, and may never write any IF, allow me following advice: things that read like the output to a sequence of commands might best be left as... the output to a sequence of commands. If nothing else, in a work this small, it'd give it more of a chance for atmosphere and exposition.
All the locations I was able to discover consisted a list of the objects present. Examining those objects results in the stock reply of "You see nothing special about x".
>x crystal key
You see nothing special about the Crystal key.
I think the fact that the key is crystal is pretty remarkable. A little later the unremarkable crystal key opens a "wooden container". After opening the generic containing apparatus and performing the winning action the game does not actually terminate. It leaves you in a perpetual limbo like the original Myst, but sans conscious design decision.
Anyway, I cannot really recommend playing this one, or even rewriting it. There was no discernible authorial intent, no content to smooth out.