It has several planar articles.
The first one is about the Blood War - brings back the yugoloths and events from Squaring the Circle adventure.
The second is the Orcus-Tenebrous story - no new revelations.
And the ecology of the succubus brings back Malcanthet, now there are succubi in the 4th edition cosmology Abyss. What's most interesting at the end, Fall-from-Grace is mentioned as an example of a redeemed fiend.
Always good to hear Planescape shout-outs. The setting continues to inspire, despite its relative age.