I see a lot of hate for STEAM in game reviews on sites like Amazon, but step into any PC gaming forum and almost everyone there practically refuses to use anything but STEAM. I have to admit I'm in the latter category, but I find the polarizing nature of STEAM to be rather fascinating.
I can somewhat understand the haters' point of view. If all you want to do is simply play the game you bought, then having to install and run 3rd party software might seem a bit frustrating to me. However, I've always found the benefits of STEAM vastly outweigh the potential drawbacks. For starters, let me just say that if you're purchasing boxed copies of games that require STEAM to play, you're doing it wrong. Not only you missing out on one of the biggest things that makes STEAM so great, bypassing the retailer and downloading straight to your hard drive, but games are generally cheaper on STEAM as well, sometimes even shockingly so.
Throw in a built in community, no need to keep track of CD keys, automatic patching (and now driver updates if you have an AMD/ATI video card), cloud support for game saves, and pre-loading for day one purchases, and the benefits start outweighing the costs pretty quick.
And of course the biggest argument in STEAM's favor actually has little to do with STEAM at all. Simply put, in a day and age when it's rarely ever a question of if a publisher will require some sort of online authentication for their game, but more a question of what form that authentication will take, STEAM is far and away the least of all evils.