Mr Penumbra's biggest flaw is that it's dated. It's written with a kind of early '10s Silicon Valley utopianism which just doesn't hold up today. The novel is much better than "The Da VincI Code by way of Ready Player One" would imply, but it's not unfair to say that the comparison is accurate.

I would still recommend it if a fun, optimistic mystery story about strange bookstores, fonts, and Google. You just have to be willing to look past a style of writing that is extremely of its era. That era being the overly-optimistic, very white straight nerd bro internet of the early 2010s. It's written for a time when Google was known better as "The cool search engine company that has nap pods and skate parks in its offices" rather than "The surveillance capitalists who buy up their competition and shutter any project that doesn't immediately turn a profit".

Fun jaunt? Yes. But its charms are dull and I doubt that time will polish them.