Overrated: any Sensible Soccer, Zool 1&2, Pinball Illusions, Street Fighter II, Cannon Fodder, Gods, James Pond.
I realise lots of people love those games, just didn't do it for me.
Edit: actually, I played Cannon Fodder(s) on the PC. Sorry, if the Amiga version is much better. Need to re-visit these some time.