I reported this on GOG's official bug tracker, but haven't heard from anyone since the initial reply.

With Windows 10 being installed, I've noticed that none of the opening videos will actually play. You can get audio, but no video. The solution to it was to just skip them so that you can get to the main menu. However, once there, the entire game ran at a snail's pace rendering it virtually unplayable.

Anyone else run into this problem?

You aren't the only one. I am on Windows 10 and decided to install this old gem to get back into it and play it. However, for some reason it runs fine for the videos, yet for some reason comes to a screeching halt at the menu for whatever reason. I have tried XP compatibility and Windows 7 so far, but no luck. Anyone got a work around for this puppy because to be honest, I just really want to play this game.

The solution that worked for me was to remove ddraw.dll from the game's folder, then remove the quicktime and quicktime preferences files from the game's folder. This will cause the movies to not play at all, but resolves the slowdown issue. There are only a handful of movies, none of which are spoilery, so manually watching the AVI files ahead of time should give you an idea of why certain transitions happen in game.