ReynardFox: Mushihimesama Futari and Deathsmiles are the ones directly known to have been rejected, it gets worse too, GOG stated that they may reconsider "if the games do well on Steam". Way to kill any potential market space with a self fulfilling prophecy.
I've lost track of how long ago this happened but my bitterness about it has never diminished, and I'd probably get modded if I shared my unfiltered thoughts on GOG's curation staff.
Sarang: Gah I can't understand for the life of me how they have this attitude towards Cave shooters but NOT Visual novels. As bad as the 360 did in Japan they gained a foothold among some gamers BECAUSE of those Cave shooters and how other consoles didn't have it. GOG first gained a foothold for offering old games DRM free games, a niche if you will. They would have gained even more with Cave among shooter fans. Oh and Death Smiles is the LEAST niche among Cave shooter along with one Capcom contracted. I can't remember the name but you fly old byplanes.
When you get a niche audience they are a BEDROCK audience and nothing to sneeze at as outlined above.
Sadly this happened back when GOG's curators had a more snobby pc-born elitist attitude to game releases, and they were often ignoring things that were 'too japanese, console or arcade based or simply for being "too niche". This was before GOG started letting hyper-niche stuff like Visual Novels onto the store.
It's also the main reason I am so angry at a lot of the low quality fare on the store today, because until they rectify turning down literal genre defining developers and games, I'm not going to stop complaining about the flood of low rent porn, visual novels and mobile caliber hipster indie crap.
Though I don't know if they even can at this point, as I originally said, it feels like they burned that bridge when they shot Degica down. If it was me and I was publishing true cream-of-the-crop games and I was turned down for such ignorant reasons, I would write GOG off and never feel the need to look back until I recieved an apology and a bloody good deal.