Well it's ABOUT TIME.

Until Planescape came around, about the only places lively enough to be adventured in were the Prime Material and the Lower Planes. The quick-and-dirty descriptions in the Manual of the Planes were enough to pique your interest, but that's about it.

It took them a long time to get around to the Elemental Planes, and longer still to make them what they should be -- wholly alien environments where adventurers are in constant peril and can't trust their own experience. The Inner Planes does a good job of pulling this off, expanding on previous material to make these planes live.

I will also say that this is the first time that certain planes (notably Fire and Magma) have been described accurately enough for me to have an answer when a player says "I step through the portal, now what do I see?"

Finally, I'm heartened to see that the Planescape writing team seems to have gotten over its self-congratulatory use of 1900s gutter slang. There's still some cant here, but it's controlled, and it's not put into the mouths of those who shouldn't be using it. This book is a pleasure to read.