Navagon: To each their own. I suppose it depends on what you're looking for as to what would qualify as 'good' in your book then. As for what's old and what runs on modern hardware, again I don't see the relevance as far as GOG is concerned. That's even before we get into how GOG plan to change their whole business model anyway...
A few things, for one thing, it's a waste of resources to work on supporting games that already run and are available elsewhere. For some games like Raptor, there's very little reason to buy it here rather than directly from 3DRealms, the only advantage to buying it here is the redownloads for life. And that's not really that big of a deal if you keep your data properly backed up.
And yes, they've changed their model which really renders pretty much all of this moot as we're no longer talking about old games and we're not necessarily talking about good games.
Eh, harumph, I've been against that whole thing from the start. There's still tons of Good Old C64 games, Amiga games, Amstrad games, Sinclair games, and not to mention the dozens of consoles that were in vogue prior to 1990 that they could be working on.