This topic is now going to be a rip-off of Bizzle's.

Book of Shadows is not a sequel, it's a bunch of stories expanding on the original game. Some are stuff that happened in the main time line and others are alternate time lines based around that ending which ends in a time loop. It fleshes out a lot of the characters and there's a lot of text to go through as it's more VN now. There was a decent LP of it a while ago that should be in the LP Archive if you don't have a PSP or anything.