I've been using GrapheneOS for over a year. I cannot complain about it, it works as advertised and it does it the best way possible. However, here's the list of things I find annoying/missing. Keep in mind, this is a subjective list.
some (quite a lot of for me) apps require Google Play Framework (or whatever the name is) to work properly
Aurora store tends to be unavailable randomly, which makes installation/updates difficult sometimes
some features are wonky, e.g. GrapheneOS has no issues with disabling wifi when leaving my home but I was never able to enable wifi when I'm back home.
default apps work ok-ish but it's far from good old iOS/Android experience