Don't know if this applies to the new GOG achievements thing in general or just this game but they don't seem to be working properly.

EG. got the achievement for defeating Hogre at a random moment in the Wolf wood level, and didn't get the achievment despite not using the flame sword on the Highlands level.

Just me?

I just successfully did the requirements for the the Down Boy achievement twice. To be extra safe I even made sure I didn't take any damage at the hound which doesn't count before the boss room, and completed the level with my health bar 100% full. And the Achievement still never popped anyway.

Like the OP said, the question is: is this a general Galaxy issue, or a Slain-specific issue?

EDIT: After I noticed Achievements not working in other GOG games too, I looked into the problem deeper and discovered that the Galaxy-related Windows Services had been disabled on my system. After I re-enabled them, then I started to receive Achievements again. So that may be the solution to the problem that others are having too (but I can't say for sure).

I've had issues with a lot of achievements not unlocking. I beat Hogre and it didn't give it to me, but it gave me the one where you kill him without getting hit. I have no idea why.