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.