Unexpected results, positive and negative, appear to have postponed the game's development

Valve has remained silent about the Half-Life 3 project due to significant unexpected occurrences during the game’s development, the company’s managing director Gabe Newell has explained.
Newell, who co-founded the company in 1996, discussed the unannounced Half-Life project without mentioning it by name. He instead spoke at length about ‘Ricochet 2’ – a project that likely does not exist – in what appears to be a code word for Half-Life 3.

“In terms of Ricochet 2, we always have this problem that when we talk about things too far in advance,” Newell said.
“We end up changing our minds as we're going through and developing stuff, so as we're thinking through the giant story arc which is Ricochet 2, you might get to a point where you're saying something is surprising us in a positive way and something is surprising us in a negative way, and, you know, we'd like to be super-transparent about the future of Ricochet 2.”
In a podcast interview with Seven Day Cooldown, Newell suggested that Valve’s ongoing silence on the Half-Life 3 project was fairer to fans than exposing the project along with its various transformations and delays.

http://www.develop-online.net/news/4...e-3-dev-issues