Actual user reviews on the store page, and not "friend" recommendations (who reads those anyway?), is a great step for Valve/Steam to take. Glad to see it.
Steam Reviews have been around for a long, long time. Not sure what is new and out of the blue.
I think you are thinking of Recommendations. This is more than just recommending. This is something people can look up on the games store page to see if they feel it is worth the purchase or not.
Well they have had the forums for years. I always check those before I make a questionable purchase. Obviously some games come along that you know that you are going to buy, but others you just don't know enough about. Still though, any new opportunity to read user feedback will be welcome, even though reviews lack the true user feedback that one cant obtain in a forum.
Might be helpfull, especially since people can warn you not to buy console ports that are horrible on PC (Like Dark Souls), or at least, point you in the right direction where to find a patch, official or not, for the game.