Valve did an amazing job at building their reputation (by doing things the right way.) Very few can do DRM without pissing off people.
The switch from WON to Steam basically destoryed a huge part of the Counter Strike community (for example you couldn't play older versions anymore like 1.5)
Also Valve was one of the first company that required an online activation for a single player offline game (HL2). It was unheard back then.
Its garbage that reduces the value of games. It just increases Steam's profits.
(I also have a lot of Humble Bundle games)
What cemented GoG for me was two events: One, they got the entire classic Thief series (my all time favorite game series which won't install on modern Windows from my game discs) and two, when a few games on Steam that I thought I owned were pulled or otherwise tampered with; something I paid for was suddenly gone or altered with no recourse. I still have my Steam account and I do play games on it, but going forward all of my game budget goes to GoG and thrift store finds.