Finally, a way to pay for a mod
Black Mesa, the loving recreation of the original Half-Life, has just entered Steam's Early Access program with a price point of $19.99. There had been a countdown on the website leading up to today, and many speculated that it was going to be the full release of the game, but those people are now severely disappointed. The first half of the mod was released in 2012 for free, and was well received by most everyone.
It's an interesting use of the Early Access program, since most everyone is simply looking forward to the single-player aspect of the game and will want to hold off until it's done. According to the Steam page, the first "~85%" of the game is complete, and the last 15% will take a "considerable time" to get it up to their standards.
Personally, I see this as a nice way to contribute to the development of a game that people may be emotionally invested in, considering it's been in development forever, but I don't see it as a game I need to play before it actually releases.