*Disclaimer, I have not used GOG is almost a year, so I am not giving a full 5 star review, I will update my review when I've checked my account again this week.*
I've placed multiple orders with GOG and had no issues with downloads or getting any of the DRM free games to work on my computer. I've been running a windows 8 / windows 10 computer and all of the games I've ordered have downloaded and played without a hitch. I do have some games I have not yet attempted to install that are part of their 'free' games on gog.
One thing I did notice was that some games (Like starwars battlegrounds) do show that they're still multiplayer capable, however the servers for that game were shut down by the origin company. So while that was at one time an online game it no longer has multiplayer support. I think with games like that they should update the site to show the game lost it's multiplayer options so anyone looking to purchase those games won't assume there are servers for them still. So while prices and games have been great so far for me, I know that some things like online games still need a bit of research before purchasing since things that start off 'single or multiplayer' can sometimes change to single player only and gog hasn't kept up.