What about Elder Scrolls: Arena, and Elder Scrolls II: Daggerfall? Bethesda is already offering them for free, so it'd be nice to see them in GOG's catalogue.
i don't think that those games are obscure or underrated.
they are just really, really old.
besides, arena is only so-so good, and daggerfall is so buggy that it's kinda silly to play it without fan-made patches, so anybody who wants to play it will probably want to go to all the extra trouble of hunting down mods/patches, ect.
i do agree that it would be nice if gog could package mods and make daggerfall (among many other games) available in a different form, but something tells me that there are all kinds of ip rights-related issues with packaging mods and so-forth.
as it is, it would be hard for anyone to charge money for either game, and a support nightmare waiting to happen for gog if they even offered it free.
btw, dagger XL is pretty awesome, if you are into that sort of thing... it looks like they are making some serious progress on it.