The most annoying thing about iPhone Maps for me is the inaccuracy of the direction indicator. I've googled and it doesn't seem to be a universal complaint even though I've experienced this on multiple devices over the years even after following instructions to re-calibrate multiple times. Maybe I've just been unlucky.

It intensely frustrating to use maps for direction finding while walking or cycling when the app is telling you are facing one direction when in fact you are facing another.