When I tried using <dialog> for the first time, there was one major thing that stuck out to me as a bit of a problem with how it is implemented:

It has become a norm to expect that if you click/tap on the backdrop of a modal/dialog, it will dismiss the modal/dialog. That isn't the case with <dialog> by default, and you need to use either use a hacky JS handler that checks the bounding box of the dialog (because the backdrop click events just end up fed to the dialog element), or use an attribute, `closedby`='any' that does not work on iOS and has spotty support at best in desktop Safari