I just downloaded Half-Life: Source from Steam after reading this (never bothered to download it before as I like the authenticity of the original). Surprisingly, I have all of the exact same errors that you described. The weapons look like they're covered in shiny plastic wrap, scientists freaking the hell out, everything. So it's not just you, the game really is bugged.
I'm on Windows 7 Home Premium x64, with a Radeon HD 6790 and a Phenom x4 955 BE. I don't have these problems with any other Source game. Or any other game in general, I might add.