From here? Septerra Core. It managed to make a series of design decisions that in combination made me not want to play it. I'd love to know the story, but I'm not going to suffer through the rest of the game to discover it.

Not from GOG? This bad gamble out of a bargain bin: The Ring. I did finish it, but I regretted wasting the time afterward.

Recently, Strong Bad's Cool Game For Attractive People. I liked early Telltale's point-and-click Hector: Badge of Carnage, and at one point I remembered liking Homestar Runner, so I decided to give it a go when it finally came to GOG. But apparently my sense of humor has changed quite a bit over the years, because I just found it gratingly unfunny. I struggled through one episode before quitting. At least I didn't pay the full $20 price.