Half-Life 2 is a great game, and Valve know this.
Valve are a really smart bunch of guys. With the imminent release of The Orange Box, I've come to realise this.
They put out Half-Life 2, and Episode 1 to get players hooked, and then when Episode 2 comes out, they put it in a bundle. This bundle contains both Half-Life 2 and Episode 1 as well as a couple of other games. People that already own the game and Episode 1 can give out their extra copy to other people for free. This, in turn hooks them on the game, getting them to inevitably purchase The Orange Box, getting another set of free gifts of HL2 and Episode 1. They then give it to someone else, who eventually buys The Orange Box themselves. It's one big giant circle.
Their ultimate plan was to get Half-Life 2 in to the hands of EVERYBODY.
And I don't think they'll fail.