Take this one with a grain of salt, but word has it the next title in the Half-Life series might not follow the same template as its predecessors. According to a story by French website Le Journal du Gamer, which has already been linked extensively around the web, Half-Life 3 will be an open-world game.
No, I'm not kidding.
The story, which is in French, credits a "trusted source who wishes to remain anonymous" for the scoop. It claims Half-Life 3 will be imbued with RPG elements like side quests and an open game world, not unlike Bethesda's Elder Scrolls games. Development is described as "well under way," albeit "very chaotic." (Valve purportedly restarted work on the game multiple times.) According to Le Journal du Gamer, the game is "very likely" to come out after 2013.
Now, I've never heard of Le Journal du Gamer before, and the story seems almost too implausible to be true. Nevertheless, it's been picked up by sources like the International Business Times and IGN, so perhaps there's some nugget of truth to it. If so, those guys in France must have some pretty good connections—we haven't heard a peep about Half-Life 3 in the past few years.