Hey there.
I just read an article on the German website welt.de. They wrote about a mod called "Black Mesa" based on Half Life. I downloaded the files and Source SDK 07 to run it like it was described. I have never really played Half Life but while I started it for just a few secs Frieda messaged me on Steam and said that Black Mesa was planned for several years and is a huge project worth sharing it with you guys.
I missed taking some screenshots and Im too lazy to run it again but there should be some trailers on youtube.
The official downloadlink is on http://release.blackmesasource.com/.
Regards from Cologne