Absolutely loved Type Help
As I churn through this pile of database/research games I bought a few weeks ago, I took some time to play Type Help, which is free, and absolutely one of the best in the genre.
It's difficult to talk about without spoiling, but I'll say that there's a wonderful focus on a single mechanic (inputting filenames) and that most of the mystery and its twists are connected very directly to that mechanic. You build understanding of the story and the filename input stuff at the same time, together, with a wonderful kind of rising momentum. It really is special!!
I also really liked the writing. It's delightfully genre-y. Every character's voice is so clear, and it often is possible to predict their behaviors quite accurately based on well-signaled habits and flaws that they express in the early part of the game. This is the same pleasure that readers get from successfully predicting whole or partial solutions to the mysteries in a novel. It's fun stuff!
You can play it here. It took me about 4 hours to complete. And once you finish it, check out Andrew Plotkin's writeup about it here.