For me, it has to be Alien: Colonial Marines as it’s terrible due to inconsistent frame rate (moments the game ran smooth and times where lag was insane, even with the best hardware). Both player & enemy AI is crap since the combat wasn’t even that immersive plus Xenomorph AI isn’t as intimidating due to it being poorly implemented.
E.T. was such a bad game. I still have my copy. What’s funny is that at one point I ended up with two copies because one of my friends left their copy at my house, but no one would claim it so I have no idea which friend it was (four of us owned a 2600). I can think of nothing more damning of a game than this example.
Edit: In case anyone wants to see what a surviving copy looks like, here is mine https://imgur.com/a/bcDxAbt