I don't like the online requirement,but after suffering through Battlefronts activation system, and Starforce before that, I'll take Steam's setup any day. It takes some liberties away, but gives some back that other publishing companies do not.
No more worrying how many more activations I have, or how many PCs I can install before some magical limit is used up. No more monitoring the hard drive space to see how long until I need to buy a new one. Install a game, play it, delete when I move on, and if I take a fancy to it again DL once more. They use Cloud savefiles, and there's no need to reauthorize something I've owned for years. All automatic. As are updates.
Add to that the sheer number of games available for purchase, the constant deep discounts (I bought Train Simulator 2014 and plenty of DLC during the recent sale...I would never have purchased what I did for the wholesale $400, but at $50 I could try it out without being worried if it didn't deliver...it does, btw, so lucky me), their support of Independent developers, their focus on listening to their customers/community, and their constant efforts at upgrades and innovation to the way they sell and the way we buy...if I've drunk any Kool-Aid it's the Valve-flavoured kind. Valve knows online, geek-oriented, gamer-oriented customer service like no one else in the biz. They have massive loyalty because they earn such loyalty.