If Congo has become an in demand title, I love it because that leaves better titles for the rest of us! Congo isn't quite that bad though.
Waterworld is pretty bad but I haven't played one in real life, so I can only assume by looking at the layout. People & places I come in contact with actually have taste & don't have crappy titles usually!

Popeye gets a bump for me if only because it is of the "superpin" bloodline & looks to be a fun flip & could be decent in a larger collection.
So... Gilligan's is probably the worst B/W I can think of. Overall I might have to give the worst title to Robocop. TMNT & Space Jam are pretty bad from DE. & for Sega, X-Files is a waste. Star Wars Trilogy & Lost in Space are pretty bad too apparently, haven't played those ones personally though.

Of course Stern has a number of bad games too.