Well...
LucasArts/Disney arriving here was a very, very pleasant surprise. The greatest achievement for GOG.com that I have experienced as an active user.
The Galaxy client excites me a lot, especially the possibilities for multi-player. But it poses a potential thread as well, there is no denying that, so I'll wait for the actual release and form an actual opinion then.
The addition of support for Linux, being a Linux user myself, was and is great too, though the extent of that support seems still questionable to me.
There are a few things that bother me, but are little more than minor annoyances most of the time: slow patching and many, many bugs with the website. It simply feels unprofessional.
Then there are the movies and the redesign of the site... I don't care, really, not even the slightest bit.
But, there are two things I hated, one being the addition of sort-of DRM in the installers, which thankfully has been removed again, after many users here complaining. So, that one is good and done for me now.
The real bummer though is regional pricing. The single worst decision GOG.com ever made. It is unjust and arbitrarily, a violation against their own former ideal. I will never buy a game with regional pricing here and still hope, against all common reasoning, that they will change their mind some day.