That frankly makes no sense to me. They're basically licensing the source code itself? I mean, if ESF was stand-alone, and free, by downloading it you could only play ESF, and not Half-Life, even if it is Half-Life's source code. If you wanted to play Half-Life, you'd have to buy it. Now, I understand that the source code is also someone's piece of work, but does Valve really need more money that they have to sell a 13-year old game, just for its source code? I say release the damn thing. Valve has a lot of good new games, I don't think it's necessary for them to live off their former glory.Id released the source code to their engine, Valve didn't. Thus the only access the team will have will be to the modding tools.
And frankly, I think that it's a bit unfair that they're making so much money on the count of someone else's hard work. People like the ESF team bust their asses to make a REALLY good, free game, with no personal gain whatsoever save for the shear pleasure of it, and Valve makes money off that. But hey, that's just my opinion, I don't think it's right.