Yup, there are several reasons I'm looking forwards to this as well. The creepiness at night being one of them.
Having a mystery to solve also sounds really enticing and I'm very glad indeed that only the game graphics are being used, as I don't know how to play games with altered graphic/textures/models and wotnot on the Mac - and nobody else seems to know for sure. So, this mod's sticking to the game graphics is fine by me.
The day / night cycle also sounds really interesting. I wonder how big the contrast will be in the atmosphere during the two different states.
The video shown so far look really god, and I've been particularly impressed with the lighting.
And lastly, it will be good
So, to summarise. Can't wait!