the design thing that i notice about most microwaves is that some of them let you just punch in a time and hit start, while others make you hit "cook" first.
i find this to be an excellent example of (failing at) optimizing for the common case--probably >99% of the interactions people have with microwaves are pure timed-cook-at-100%-power, and requiring an extra button press to enter that mode is silly.
Some let you just press the "add minute" button and it immediately starts cooking on a one-minute timer. Want to cook for more than a minute? Keep pressing that add-minute button while it's cooking.
i find this to be an excellent example of (failing at) optimizing for the common case--probably >99% of the interactions people have with microwaves are pure timed-cook-at-100%-power, and requiring an extra button press to enter that mode is silly.