GOG is DRM free!
Even if GOG closed down tomorrow, I could still play the games I'd bought from them. Can the same be said for Steam?
Also, with my GOG version, I have full control over the patching process. If a new patch breaks the game or my mods, I can choose not to install that patch. I don't think Steam users have that luxury.
No, I'm afraid the reasons for not using Steam are just too many. And I for one will never buy a game from Steam.
I'm amazed this thread got this far before someone mentioned the DRM aspect to Steam...;) I've got to agree with Klixen.
The chief problem with Steam as it currently is setup is that you have to go online in order to initiate off-line mode. Basically, if you are not already in off-line mode, and your Internet connection goes down, you can't play any of your Steam games. Gog is a huge advantage over that--and I own both Steam and Gog titles. Gog stuff plays anywhere, anytime.
IMO, whether you use Steam or Gog, your downloading bandwidth will make a lot of difference--so get the fastest Internet access you can afford. Truth is, if you have fairly poor Internet access bandwidth--you need to be buying on disk whenever you can. The world is a long, long way away from being universally wired so we can count on games continuing to be available on disk for quite sometime to come.
The *problem* is that, increasingly, game devs and publishers are turning to services like Steam to deliver their goods--like Skyrim, for instance--you cannot buy a non-Steam version of the game IIRC. You can get it on disk, but it still runs through a Steam account! Still, for people with slow Internet access, disk is by far the best way to go, imo.
I have a separate folder in which I keep all of my Gog titles in their installer state, along with any patches and so on, quite apart from the space required to actually install my Gog games. My folder is "GOGinstallers" and every game has its own sub-folder inside that main directory--so if I need to reinstall I don't have to go to Gog again and re-download the game--I already have it available. Everyone should be doing something similar. Don't have enough hard drive space? Then buy a bunch of blank DVDs and keep your master Gog copies there.
My Internet access averages ~5MBytes/sec (not bits), so is pretty fast & quick, and I sympathize with people who have slow ISP service. I like the way Gog does its thing because I'd rather have a new installer version of a game than have the old installer version with umpteen zillion patches to keep up with...
Gog's specialty, remember, is "Good Old Games" and it's a blessing for people buying them for the first time if they can download the latest version without having to worry about patches--all of the old games Gog sells are fully patched when you buy them--download once and you are done. Also, when Gog sells an older game the newer installer versions are deliberately enhanced to improve compatibility with the latest OSes..all of the 2.x Gog installers are now compatible with Win7/8, pretty much. I downloaded all the newer installers for my games...;)