I would probably put Ninja Gaiden and Probotector (I think the Yanks call it 'Contra') up there. Never owned Probotector, but I managed to finish Ninja Gaiden 3 times with all the scarabs. So hard to push through, but once you figure it all out, it is so rewarding. Still haven't tried 'Master Ninja' level yet, and NG Black hasn't come out in Australia yet either.