FYI/FWIW:
I swear I thought I posted something years back about this (the darned thing still isn't completed yet) which I was going to reference here but I can't find it. There is a new trailer on YouTube for this total conversion of the original Half-Life using Half-Life 2's Source Engine. The trailer contains some gameplay. The official website is: http://www.blackmesasource.com/. Can't wait for it to be released.