Memento Mori was first created as a paperback book, where progress through the game aspect was documented in checklists printed at the back of the book. Key findings and page numbers could be written down to help track progress. Now, most of that is done for you with some simple code tracked by your browser.
Most gamebooks involve reading a portion of text, then making a choice on how the protagonist should behave. This is similar, but you will find less action and more atmosphere. Also unlike traditional gamebooks, this story requires that you find multiple keys as you read to open alternate routes. Furthermore, reading is not linear; some paths can't be reached without keys, while some paths can't be reached at all. Cheating in Memento Mori isn't just suggested, it's required.
You can think of this story as a sort of homage to the Schrodinger's Cat thought experiment, where multiple different realities are coexisting in the space of uncertainty. Only by completing every chapter, opening every lock, and exploring every option can you dispel the uncertainty and open the box.
In regards to the passages written in Latin, I must confess to less than minimal knowledge of the language. Some of it might not make sense or might now mean what I took it to mean. At times, you may have to just accept my apologies and humor me.
Finally, I am aware of other stories of the same name. The movie Memento was based on a story of the same name, and the author of The Prime of Miss Jean Brodie also has a novel of the same name. I didn't know that when I named mine, but I have no regrets or intents to change it. We can all share.