I remember karateka- it was the first action game I saw on an Apple. It was one of several games (Ultima being the other) that really made me want to learn assembly language and program hi-res mode Apple graphics. I got stumped by the weird system and never really learned how (Romero was obviously a lot closer to understanding). I didn't even know that Mechner made Prince of Persia, until I read about it a few years ago (I ignored the PoP game series).
I have an Apple IIe next to my work laptop right now running Ultima IV. I recently replayed Karateka all the way through (it's not that hard).