I want to suggest to make outstanding Invisibility effects like it was done in "The Lord of the Ring" movie.
(when Frodo take on the Ring and was pierced by poison dagger by one of the nine "Ghost-Kings")

When you cast this spell you will have:
- inverted gray-scale view of the environment;
- with some blur effect;
- some underworld sound effect;
- slow-motion effect.

You will feel yourself like in parallel dimension.
I think Oblivion Graphic Extender can help a lot to make proper effects (it already have nice shaders)

Maybe some of experienced modders can create this awesomeness ?