I've been thinking about this thread a lot to come up with some of my worst games ever, and I've realized I haven't played many bad games on the Amiga, so here's my 3 games that were really bad due to some particular issue involved.
Shadow of the Beast 2 (the most unplayable game I have ever seen, can anyone get more than 5 minutes into the game without God mode turned on?)
Maniac Mansion - I loved this game on C64, unfortunately, the amiga one looked like it was a rip of the nintendo port, colors were all messed up, and the music truly sucked.
My other is The Krystal - probably Cinemawares worst game, mind you, IIRC they only published it. It was perfectly playable, it was just...bad.
