Check them out in this promo video from GOG
A lot of them don't qualify as adventure games so the Darksiders should be interested, too.
There is a really interesting Indie platformer called Puddle for $7.99. Eureka!
But for adventure gamers, Deponia 2 is $13.99 on preorder or you can get 1 & 2 for $23.98. Not bad!
Oh, and GOG has 50 games for Macs. Buy one and you get the PC version free with it, and vice versa. The Witcher series is among them and games like Sim City 2000. They also have 8 free games for Mac, including Beneath a Steel Sky.