Not sure I should list any, since maybe I was just one step or one search away from getting them working.
But what the hell. ; )
Eador: Genesis was a no-go on my old laptop. Haven't tried it on this newer one. Suspect it will be fine, but that requires trying it.
The Guild wasn't cooperating. At first it wouldn't do anything, then I managed to get sound. I think I finally got a menu to come up, and then I gave up in frustration.
Space Rangers 2? I think it was 2. Some of us had the same problem, unfixable, where I think we were getting sound but no video. The developer themselves fixed it later on with a different version (had an expansion or something) and I think that solved this particular problem for everyone. By the time the new version came to gOg, I had already found it for cheap at Half Price Books.
I haven't put much effort into it, but thought I would give Kohan a whirl from my disk. Nothing. Haven't bothered searching for solutions, but did try the usual easy suspects: compatibility mode, run as admin, yada yada.
Might have been a few others here and there. Surprisingly few problems in the old games I've picked up here, so good job, gOg! Really appreciate your efforts on this.