Well it's really a pretty minor thing but there's a specific type of defensive ability in this game that has been annoying me for the whole 2 years that I've been playing this game.
I'm talking about defensive abilities like addle and feint that only apply to either magical or physical incoming damage. The problem with abilites like these is that as far as I can tell there's absolutely no in-game way to tell wether any attack is magical or physical in nature (and some are just really unintuitive). So just give us some indication at all on wether an attack is one or the other. Could be as simple as a little icon next to the castbar.