I don't like Steam -- what about Joe Blow who has a laptop that has not I-Net Connection there and puts HL2 on there? Guess what? He's been ripped-off b/c he can't play his SINGLE PLAYER game offline. SINGLE PLAYER means alone -- so, I should not have to go online to authenticate a product I purchased. SINGLE PLAYER portion of the game should NOT require Steam authenication -- end of story.
Multiplayer is another story, since MP does require a connection.