Niggles: GOG needs to add the ability to actually play or sample a soundtrack before purchase as well instead of us having to look for it on youtube or bandcamp first....
Exactly, and because they don't I rarely bother to get a soundtrack that isn't included with the game, whereas I might otherwise. I'm certainly not gonna traipse all over youTube finding soundtracks.
Perhaps they don't, because way too many are crap and they would sell less if people didn't take a gamble.
Filtering is a great idea too, but GOG are not known for finishing features properly, let alone adding new ones.
DEVS or music artist should really provide a video clip, that features short segments of the songs, maybe along with game artwork or development photos.