I just did today's word and I thought this was pretty fun. M⁻¹M stumped me for a while, but once I got it, it gave me a good chuckle for how obvious it was in hindsight. I do work in physics, so that gives me a head-start on recognizing all these formula. From the other comments here it seems enjoyment is very correlated to amount of these formula one already knows.

Anyways looking forward to checking this the next couple of days