For me, I was most disappointed in Turning Point: Fall of Liberty. The premise was fascinating and I looked forward to it. They put out a demo on PS3 and it seemed okay. The launch game was worse than the demo. Just garbage. I finally actually played the entire game like 15 years later. It was very interesting and worth a lazy play, but not a very good game.

Otherwise, bad games to me are ones that are just endlessly difficult and frustrating.