So, you're looking for pure fluff setting material, not crunch books? I recommend the Codex Arcanis, from Paradigm Concepts. The book is ALL setting (crunch is a couple of pages in the back.) It's the counterpoint to the Player's Guide to Arcanis, which is mostly crunch with some setting stuff.
Arcanis works on so many levels. On one level, the opportunity for a pure hack 'n slash campaign is rich with vast evil empires to the south, ancient ruins from long-dead civilizations, and recently (with their book Legacy of Damnation) the opening of the Sealed Lands, which are still controlled by the demons who once haunted the land. So you've got your epic adventures and horrible villans.
On another level, you have the political intrigue. Arcanis, unlike most settings I know, doesn't put its nations into the "good guy" and "bad guy" setting. There is no clean deliniation. The nations of man (and the Dwarven enclaves, and the Elorii nations, and the Ss'ressen lands,) do not see eye to eye, and while all have been good at some time or another, all have also been bad. Political intrigue is the order of the day, so those looking for a deep storytelling campaign would love Arcanis with its richly detailed nations, personalities, and storyline.
Finally, Arcanis is about the apocolypse. Beyond the political machinations of the human lands and the evils of the Serpent Empire and what lies sleeping in ancient Myrantian or Auxunite ruins, you have the big bad. The Silence, and their shock troops the Voiceless Ones, fighting a neverending war with the gods that, by all accounts, they are slowly winning.
This would be too much for a normal campaign, but Paradigm Concepts manages to actually fold it all together into a remarkably well-written storyline (told and influenced via their Living Arcanis campaign.) So if your friend is looking for sheer setting, definitely take a look at Arcanis.
The Player's Guide to Arcanis isn't a bad look either, adding classes like the Patrician and the Priest which helps round out the roleplay aspect of d20 a bit more (the Patrician is a nobleman, not really a fighter more of a talker. The Priest is a follower of the gods geared more towards healing and inspiration than the battle-ready Cleric.)
Of course, if you like the combat you can take a look at the Holy Champions, also in the PGtA. A different core class for each god. And a whole ton of prestige classes that cover a whole lot of ground.
