GOG is SO MUCH BETTER THAN STEAM! With GOG you buy the game, YOU OWN THE GAME. Download it, store it on your own hard-drive, burn it to your own DVD-R's, stick it in your cabinet and install it 10 years from now, or 40 years from now. With STEAM, you buy the game, and then you HOPE that STEAM keeps it on their server because otherwise you can NOT play it. With GOG you are buying the game, with STEAM, you are buying "access" to the game on their network, but only for as long as they keep it on their network.
Being able to play any of my GOG games WITHOUT an internet connection is a HUGE reason why I love GOG and I only "tolerate" STEAM for a few games. I travel a lot for work, so when I get stuck at some work site, 40 miles from the nearest town, and then have to wait 2 days for some inspector to show up and sign-off on our work, those 2 days go a LOT faster when I have some GOG games on my laptop to keep me busy. My STEAM games require that I log-into STEAM... NOT gonna happen when I am 40 miles from the nearest internet connection. GOG beats STEAM once again!
And speaking of STEAM's network, every time you play any game on STEAM, they record WHAT you are playing, WHEN you are playing, and HOW LONG you are playing, and every thing you DO in the game. Oh, but people want those "achievements"... yeah, sometimes, but with GOG I have the choice to play through GOG GALAXY and keep track of all those stats and achievements (and more), but I ALSO have the choice to play OFFLINE, so that there is no permanent record that shows I played INDIANA JONES for 200 hours that year, and my wife wants to know WHY I never have time to paint the back desk, and my boss wants to know WHY I won't work more overtime, and OMG look at all the hours this guy wasted on video games! I like that I can keep my gaming time PRIVATE on GOG, by just playing OFFLINE, and NOBODY is keeping track of ANYTHING I do. SO NOBODY can use it against me later!
ALSO with GOG, you often get TONS of EXTRA FEATURES and supplements that you can NOT get on STEAM. GOG often includes the game's complete soundtrack as Mp3 or FLAC or BOTH; you often get artbooks, early concept art images; interviews with creators; additional in-game equipment or perks; PDF versions for manuals and reference guides, and Strategy Guides ---- and TONS of stuff you usually do NOT get when you buy the EXACT SAME game through STEAM.
ALSO with GOG, you get TONS of free games, and some high-priced premium games are handed out for FREE several times each year for various promotions. I've got several $40 games that I NEVER would have purchased, but since they showed up on a FREE promotional give-away, I decided I'd give them a try.
I have tons of games on GOG, and only about 7 on STEAM, because the ONLY reason to buy from STEAM is if that particular game is NOT available on GOG.