Ptolus has completely reinvigorated my campaigns. There's so much material in this book, I don't think I'll ever fully exhaust it. It's become my favorite setting and I measure all other supplements to its high standards. Ptolus works well on its own or as a drop-in into your setting of choice. There are specific adventures included and backgrounds and history for a number of 1-20 campaigns.
I've been using the PDF version for almost 2 years now as it's almost impossible to find a hardcopy version. I highly recommend checking this product out.