I like GoG, a lot, but one of the games I bought there doesn't work well, namely Beyond Good & Evil, the video is out of sync with the audio during cut-scenes, the video plays at a very accelerated speed while the audio plays normally, so the dialog cannot catch up to the events unfolding at high speed. I did have other issues such as flickering textures but those were fixed by selecting specific options under the compatibility options in the game's launcher window (hardware vertex processing and so on). But the out-of-sync video and audio issue persists whatever I try to fix it, and because of that I can't play, since the game works in such a way that the cut-scenes suddenly stop to leave place to game-play, and then the cut-scene starts again, that way I lose pretty much everything in terms of story telling and I have absolutely no idea why I'm doing what I'm doing, all I know about the story so far from what I managed to understand is that there's an alien invasion somewhere and there's that girl and that pig-man trying to do something about it.
But it's the only game out of those I bought there that really doesn't work well at all, the others I have (Fallout, Fallout 2, Earthworm Jim 1 & 2, MDK2) all work well (although I did get a few freezing issues in MDK2 during cut-scenes, but it doesn't happen all the time and I can't provoke it). They are doing their best to make old games compatible with today's hardware, OS and drivers, but it must be very difficult to do that, and I don't expect them to be perfect either, I'm just glad I can buy those games in the first place and at such low prices, I could be going to a fast-food restaurant and spend more money there, so I can't really complain. I did send a help message about my BG&E issue but so far no official responses (a week later), maybe it's related to my system, but I wouldn't understand just why, nothing is over-clocked, everything in the BIOS runs at manufacturer's default settings, all my other games work well, no BSODs, no OS-related issues, all is well really. The games I want to see at GoG are both Turok (Dinosaur Hunter and Seeds of Evil), along with Shadow Man and Powerslave (also known as Exhumed).