I find EMs to be incredibly challenging. Short games usually - especially with features (or lack of) like no ball saves, tilt doesn't kill the ball but kills the entire game, and gobble holes. Competing on one is similar to other simple games like pitching horshoes. The old "easy to learn and difficult to master".
From a technical & repair aspect, they really fascinate me in the internal workings, how they made gears and relays perform like a rudimentary computer.