Engerek01: GOG downloader is (was?) awesome and I never had a problem on my over 300 games i downloaded. However Galaxy had problems with my each try with only 10 games.
Problems with Galaxy:
1. By Default it doesnt download the installer but the game unpacked. This means lets say Witcher 2 installer is 10 GB and it becomes 20 GB after installation. Galaxy downloads this 20GB
2. Galaxy has an amazingly low download speed on my any locations and any computers. Even downloading the installer directly from the web is a lot faster and stable.
3. You can choose to download the installer from the Galaxy by going extras and backup files. However this never concluded on my tries. It always failed on all my tries on all my laptops.
4. If you choose to install the game on its default way through Galaxy, there is a high chance that the game will be corrupted and game wont work. I constantly read about other people having the same problem.
5. Even if you didnt install the game from Galaxy, on some games Galaxy automatically recognize your game and add it to your Galaxy list. This is fine but then it tries to update it which almost always corrupted the games for me. Also for games like Baldur's Gate, the update process removes all the mods.
6. And even if everything goes fine, the game might just not work through Galaxy. 5 of my games i have on my laptop now work fine on its own but crash whenever i try to run them through Galaxy.
I reported these all on mantis and i have complete faith that it will be fixed some day.
And I have over 100 games installed in Galaxy and have had very little issues. The worst I've gotten is some hard-drive related errors which usually is fixed by restarting the download, and haven't even had those in a long time. Might I ask when the last time you used Galaxy was, just find it strange how I can have nearly a bug free experience and you get all of this.