I've heard many complaints about the price of steam games but I've found that most of the time it is cheaper than buying the retail version of the games e.g. Bioshock £3.49, CS:S for £6.99 (I think) and the old Half-Life expansions like Blue Shift and Opposing Force. Fair enough these are sale prices but they are still cheaper than buying the retail version in the sales.
Also, I like that steam has changed to local currencies now. It means I don't have to pay a £1.50 currency conversion fee along with American Tax everytime I want to buy a product and I know exactly how much my purchase will be.