Difficulty is largely dependent upon how good a player you were, and what DIP Switches had been used. Basically I'm not very good at any of them, so find the likes of Tapper difficult enough - I can do three or levels, but that's it.
I used to love watching people playing Defender. If you found someone who was good, it was really a sight to behold. In this day and age of Mame and controllers, I'm still utterly horrible at the game.