In all of your games death never feels frustrating, not even in Isaac where it's permanent, are there any design decisions that you make with this in mind?

yes, its the focus of most of my designs, i hate frustrating games and there are many ways to design around this that are just basic logic, like removing penalty but raising difficultly, making the game very replayable so dying isnt much of a penalty, giving rewards for replaying and keeping the difficulty curve very well balanced.