Manual of the Planes was a good effort. It's my springboard. But the book is rendered un-usable due to many contradictions, omissions, scattered information and, most importantly, all the crunchy bits being completely buried in dense walls of text.
Yet, the guts of the book are inspiring, packed with wonderful ideas that were both new and (back then) old collations of articles from Dragon Magazine.
I have begun the arduous task of condensing Manual of the Planes down to a comprehensive ref sheet, not only so that I can understand the rules of each plane at a glance, but so that I can make NPCs that are knowledgeable of the planes actually SOUND knowledgeable.
Here's a glimpse of what's taking up my time since the completion of the table:
I plan to make this available for free once it's more complete. It covers all 82+ planes listed in MoP (though I've ruled that the plane of Electro-Magnetism no longer exists). I've also replaced Olympus with the Dream Lands (which was Olympus' pseudonym anyway).
Only with such a reference sheet did I feel like I would be able to DM properly the potentially rapid shifts in environment of planar travelers.
Stay tuned and I'll do a bigger blog post once it's ready for use.