Fan-made sequel to Opposing Force features credited Half-Life voice actors

Is there any other game series where fan-made content feels as legitimate a part of the fiction as Half-Life? Perhaps the runaway success of Black Mesa has skewed my thoughts on this, but I've found myself paying a lot more attention to how the community is playing with the Half-Life story of late. On that note, I'm particularly intrigued by Through The City, which pitches itself as a direct sequel to Half-Life: Opposing Force, set during the events of Half-Life 2...
Read more.