Animaitor: Great game and even though in game achievements are nice, I totally agree with PACmanDRO. It should be mandatory to add achievements to GOG releases if the Steam versions already have them. So many games on GOG are missing achievements is embarraing...
Berzerk2k2: I rather have them in game and actually working than in GOG Galaxy and being broken once more (like it is the case with many other games here). Also in game achievements can be unlocked again when you start the game from 0 again. Once they are unlocked in Galaxy there is no way to make it happen again because you can't reset them. You also don't need to have Galaxy running at all to unlock them in game. Personally I think the way it is right now just works better.
If the achievements were in the Galaxy client and In-game, couldn't you still re-earn them in-game if you deleted your save file, but also have Galaxy track your lifetime achievements? I don't see how you're happier with fewer features. If you only care about in-game achievements, then what harm does it do to you for us to have them in the Galaxy client too?