Before we go on, I should warn you that I will not be talking about how sharp this lens is. In fact, let's get that out of the way first. The 40mm pancake is more than plenty sharp for $200 price range. whether it is sharper than EF 35mm f2, EF 50 f1.# non-L, and sigma 30mm f1.4, is not my priority. There are other lens tests out there for that. I have a certain sharpness tolerance that may differ from others, but this lens gets a passing mark on sharpness.
Alright, now let's go on with other things that matter for a $200 lens.
If I were to have any complaints with this lens is the STM or the focusing motor to be exact. To even manually focus, the lens needs to be powered, meaning the camera needs to be on. The 40mm tends to stick out when it is focused at minimum focusing range, so in order to "retract" lens, you first have to focus at infinity, or do it so manually before turning the camera off. I know its a short lens, but I still wouldn't want a chance to hit anything while the lens is stuck at the minimum focusing. If this 40mm were to be a USM lens, it would've been a full manual lens like most USM lenses are.