I’ve so far not really had an issue with face id so far. It needs some distance which I always get wrong waking up, but apart from that it’s always been just point the phone my direction for it to work. There is apparently an issue in strong sunlight, but I haven’t encountered that yet.I just found more situations where it doesn't work, or work as well as a fingerprint sensor.
Waking up in the morning and having my face be all smushed and squinty would make it not register.
I also like to keep my phone sitting on a desk or counter and just open it with my finger rather than having to awkwardly stand over it so it can see my face, or pick it up and point it at myself.
And when Face ID fails to register, it's harder to know why exactly compared to a fingerprint sensor. With a fingerprint you either have gunk or water in your finger, or you didn't put your finger on just right. Whatever the reason, all you have to do to fix it is try tapping again which is pretty much immediate.
With Face ID you can have too dramatic of an expression (yawning, smushed in the morning, etc) or you can have the phone at the wrong angle. These issues just take a little too long to try to fix, you have to move your head or phone around to get it to register just right, which takes longer than just quickly retalpjng a fingerprint sensor.
I also wish Apple gave an option for it to unlock and go straight to the home screen, instead of swiping every time.
I actually like the S10's face unlock because it does have that option and it makes it feel a lot faster (I know it's less secure than Face ID, but who is going to steal my phone AND make a printout of my face?). Only issue I have with the S10's is that it doesn't work as well when I have sunglasses on.
I am making Face ID sound worse than it is, though. It is really cool when it works and it makes putting in passwords super easy.
Most of these complaints are pretty nitpicky, but I just found that at least once a day I couldn't get the phone to unlock with Face ID and had to punch in a code. When I have a 4 digit code it's not bad, but if I have my phone synced with my work they require a 6 digit one which is more time consuming to type in.
I just wish Apple had the option for a fingerprint reader too. Hopefully when in-screen ones get good enough they'll start having that as an option too.
With the fingerprint sensor I found it impossible to open the phone after a shower, even when I dried my hands for the third time. It was also hard if my fingers got sweaty.