shadowmirage: This may get me burned at the stake for heresy, but my most disappointing GOG purchase so far has to be... Little Big Adventure.
The reason for this is largely the fact that I am terrible at the game. I attempted to get through the introduction sequence dozens of times, but kept being killed or captured and having to redo the ENTIRE thing over and over and over… until I cried blood.
Finally, as the new dawn was breaking and the birds began to sing outside my window, I managed to exit the asylum. I spent a few pleasant minutes exploring the city thinking to myself, "well, that was a rocky start, but at least now I can begin to enjoy this wonderful adventure!"
Then I arrived at Twinsen's house… and got shot. When I woke up back at the asylum, my internal scream shook the monitor. Gritting my teeth, because now it was personal, I vowed I would beat this damned game no matter what! I trudged back to the house and tried to find a hiding place. Instead I got shot… over and over and over again.
After that I admitted my defeat and gave up on the game, expecting the rest of it to be just as impossible.
I had read all the hype, the misty eyed retrospectives, and considering how much I love adventure games, I expected this to be the perfect game for me. I suppose I just don't have the patience for this kind of trial and error gameplay anymore. The nostalgia factor is not there either, so I can see how outdated parts of the game are.
*dodges the rotten fruit and pebble packed snowballs*
Apart from that, I'd say a few of the Daedalic adventure games. The Deponia series and A New Beginning come to mind immediately. This is mainly due to the bugginess of the games as well as a few illogical puzzles. At some point in "A New Beginning" you are unable to continue with manual saving. The UI is often broken (especially for Mac users) and the English translation is terrible. There are also game breaking bugs. I encountered one in Deponia at the very end of the game, and never finished it as a result.
Luckily, most of my purchases here have brought me many hours of joy, so a few rotten apples here and there are bearable. :)
You've missed one of the greatest stories of the 90's. Grit your teeth and try again - you won't regret that! :>