Picked up King of Dragon Pass for a trip down memory lane, holds up pretty well when compared to my memories of it.
Basically it's a game that is (so far as I know) pretty unlike any other, and certainly very uncommon at the least. It's a civilization management game where you make a series of decisions (how many citizens do you allocate to farming, how many soldiers should you raise, should you punish the seasoned warrior who stole some wine or let him off, where should you send explorers, which god(s) should you worship, etc) which will help to guide your society.
The goal is to become the "King of Dragon Pass" which (similar to games like Crusader Kings) requires political decisionmaking more than it does combat.
In some ways it's not unlike Faster Then Light in that you make decisions and while you can make educated guesses the 'best answer' is often impossible to know ahead of time so there is a degree of luck involved.. That said such a mechanic (while sometimes frustrating) keeps the game replayable, otherwise you'd quickly learn all the answers.
There is a lot more under the hood, but that should give you an idea of what to expect. As others noted it (and, honestly, any half-decent game, much less a good one) is worth picking up for less than two bucks. I promise you that if you like the genre at all it will be more than worth it.
I tend to agree that GoG is moving away from it's start by having more newer games, however as noted they still fill the niche by having tons of old games for sale, generally optimized to work on new OS. So long as they don't drop their library of "old games" I'm totally fine with them bringing new ones into the frey.
As noted they also don't have DRM, something as far as I know no other large digital merchant can boast.