A found this review of GOG.com
It is a great review. I personally don’t like to buy games online, because I am a part time game collector. Part Time because I collect games that I like in the platform that I play (mainly PC). Basically I only buy games that I would like to play, and I am likely to play, although I might never have the time to play it. I have over 700 games.
Online services do have their main purpose with me, for example sales, where you can get a game a lot cheaper.
I never wanted to start using Steam, but I had no choice. Some games, even if you have retail package you need steam to activate the game. This is very tedious, and cumbersome. Steam platform is good. By no means it is a bad platform at all, and it has it good use for other users. I am an old fashion gamer though, where I would like to install my game in my gaming PC, my laptop, and maybe one more PC. Sure, I can do that with Steam, but I need to install the whole client, and lately it has been getting heavy (it is making my PC shutdown 7 seconds slower while it is closing Steam, even though it was not used at all).
Enter GOG. The thing that attracted me to GOG was Good OLD GAMES DRM free. I have nostalgia sometimes (I just finished playing Alone in the Dark 1+2+3 from gog) and I can buy this games which mainly work in Windows 7 64 bit. Sure, I could have used DosBox or something else to get it working, but this is all done. It is beautiful to launch the game and it runs. No tweaking necessary. One good example is Die By The Sword. I have both, CD and gog version. I can get the CD version to play, but sometimes the main menu is corrupted (buttons are not where they are supposed to be), and it is nearly impossible to click on the right button. With the gog version it just plays great.
I am building a nice collection of games in gog, and I get to re-play some of my favorites in my new PC. I definitively recommend Gog if you play games in PC (TIP: If you play in a laptop, most games will play fine, even with integrated graphics)