I think what makes a great bath is satisfying all your senses, right? If one sense is not pleased, it can throw the whole experience off. You need soft lighting, nice soaps smells, quiet, a clean bathroom, warm water... I don't eat in the bath (see Gummo!) but a glass of wine doesn't hurt.
I do like to read in the bath, and there are some books that are best. Can't be too heavy, has to be a bit of an escape from reality, but not too much or you end up shivering in cooled water an hour later.
All bath photos from Foto Decadent.