I'm not sure how much of the success it attributable to Steam, and how much of it is just a consequence of the times - lots of cheap tech, lots of people using cheap tech, and most importantly, video games being something everyone does. In the 80s and 90s, video games were for geeks. Ha, in my freshman year of college in 2001, my roommates were baffled that I would put on a headset and seemingly talk to my computer while playing a game on it?

Anyway, I will say the Steam Early Access program is amazing. It basically lets developers develop games in a Lean-Startup style, by releasing an MVP and then iterating on it, and it lets customers buy the game at any point to fund the development.

I've been playing Kerbal Space Program (highly recommended if you're interested at all in spaceflight, orbital mechanics or rocketry) on the Early Release Program, and it's just awesome. The developers are cool and are pretty at-large in the community on reddit.