Personally one of my biggest "likes" of Steam is the fact that they promote so many smaller games.
We've all heard of Bioshock 2, Mass Effect 2, AvP etc and we have in the past went out to buy these blockbuster type games in the shops.... but something like Gratuitous Space Battles would have sat on a PC Gaming shelf for several years until it was binned or sold for $2.
Steam offers up an extensive catalogue of these smaller games which have made a supreme hit with older games for their length and complexity, disillusioned gamers who find their simple addictiveness alluring and even the newer generation of gamers with cute graphics or concepts to spark the imagination.
Steam could be helping/hindering these companies into an EA-type buyout or to become more fully fledged studios producing the legendary titles of the future. Without Steam, these games may have ended up unmade, unsold or treat as a free web browser game.