I wanan buy BM but first...

What’s the difference between the $20 version and the free mod version? Other than price?

Bug fixes, new voice acting, a lot of new goodies, multiplayer maps, continued updates including the Xen chapters (when they’re done) which have been greatly expanded upon, Steam Workshop support…

Have you tried the search button? You’re not the first to ask this question by a long shot.
As stated a bunch of times, there’s a huge amount of changes and improvements, both huge and small. Additionally, MP and Xen will be Steam only.

I actually did try the search button but it kept hanging so I gave in.But thanks for the info.

Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.