This is a mod, meant to be abit creepy, but a whole lot 'o' hard! Not impossible, mind you, but hard, non-the-less. This mod gives you a full campaign replacement, however, it does not have different level names, or music. The demo including the first 5 levels should be out shortly.
Yup, that's right, I'm working on the last level of the demo. It should be up for download very soon!