The Planes Above is a solid setting supporting high paragon and epic level adventures in D&D4e, taking the Points of Letting setting assumption to cosmological scales. Heaven was broken in the Dawn War between the Gods and Primordials. Places of evil and forgotten relics are obvious targets for adventurers, tiny communities are threatened by raiders and abominations, and even Good Deities hold dark secrets.

The Astral Sea is much like you'd expect: an endless void haunted by Githyanki pirates and worse. Godly Domains serve as safe havens and larger sites for adventures. Inhabitants of the Astral come in three flavors: Exalted are dead worshipers of a god, enjoying a happy afterlife. Outsiders are dead mortals who's afterlife isn't working for mysterious reasons, leaving them stranded on border islands. And then there are mortal natives, travelers, and supernatural beings like Marut. Most of the book focuses on the setting, with some highlights being the Game of Mountains in Celestia, a tactical wargame that determines which of Moradin, Kord, or Bahamut gets to control the Domain that season, and the Prison Dominion of Carceri. There are about 40 pages of monsters, with CRs from 12 to 29, but a quick spotcheck suggests that they're built using pre-MM3 math, and so may require some conversion.

Not the most essential book, but full of cool bits of high fantasy weirdness to loot for other campaigns, and a solid expansion of the 4e Points of Light to epic-level extraplanar cosmology.