Barney Calhoun is most DEFINATELY in HL2. So is the Gman. if you want, I know of a whole slew of places to get dirt on hl2.
They hunger is a single-player horror mod for the original Half-life. Think "Half-Life meets Night of the living Dead" With some return of the living dead and occult spread through out. It is amazing to think the guys that made it did it for free.
Go here:
http://planethalflife.com/manke/
It has the skinny on it.
also, if you want to see some pics, I have a gallery on my site:
http://scaredyet.net/gallery/theyhunger.aspx