Character Options is the best part of the book. It's an extension of the core PHB options for every class, many of which were previewed in Wizard's Unearthed Arcana articles over the last couple years.
The barbarian path of Ancestral Guardian is a good one for Greyhawk characters hailing from the Ice, Snow and Frost Barbarians of the north. These people have a norse vibe to them, thus ancestors are important. I am reminded of the old magic item The Black Sails of the Schnai that summons an old ancestral spirit to aid a PC. Another good region for this path is the horse riding nomads of Ull who worship their ancestors instead typical gods.
Path of the Zealot is all about berserker action. It specifically mentions that this is a good option for followers of Erythnul and Hextor (gods of slaughter and war).
The bardic College of Glamour has ties to sylvan things like the fey. This is a good choice for elves hailing from the nation of Celene or perhaps living around the settings many Fading Lands.
The College of Swords takes bards to a more martial direction and I think that fits nicely with my ongoing Hold of the Sea Princes campaign that relies on high seas/swordplay elements.
Sadly there is only two new cleric domains in this book, Grave and Forge. Greyhawk isn't particularly known for its forge gods (unless Dwarven pantheon). Whereas the Grave domain will come in handy for those who want to make a cleric of Wee Jas the goddess of (restful) death and magic.
Fighter gets the Arcane Archer at last, a popular prestige class from 3E. This archetype can find use from the elven realms of Highfolk to the parapets of Irongate and everywhere inbetween.
Another classic D&D archetype, the Cavalier, returns. The use for this fighter option is obvious for Greyhawk given the abundance of knighthoods and noble houses in the Flanaess.
Ranger has the Gloom Stalker archetype, which fits nicely with many of Oerik's evil-plagued forests and Under-Oerth adventures.
The Inquisitive and Mastermind rogue types are perfect for those who run campaigns in the City of Greyhawk or any other place region focused on intrigue.
The Swashbuckler type for Rogues obviously goes well with my Sea Princes and south seas campaign suggestion as well.
Sorcerer Origin of Shadow Magic is good for a character coming out of the Valley of the Mage or the Dim Forest. At 6th level they can summon a Hound of the Ill Omen which many Greyhawk fans will recall from the 1E Fiend Folio.
Speaking of shadow stuff, the Warlock Patron of the Hexblade is tied to entities from the Plane of Shadow as well. The same patron responsibile for creating the infamous sword Blackrazor.
Wizards get only one new tradition, the War Mage. This will of course come in handy for characters from nearly any magic using realm in Greyhawk such as Furyondy, Iuz, Keoland, the Great Kingdom and so on. War is all around.
There is a short section on Racial Feats for non-human characters. All will add flavor to your favorite elf, dwarf or yes even tiefling character.
The section on Random Encouters is an old school DM's delight; this lengthy section covers every terrain (not climate though) including urban and underdark. You can't get enough random tables.
The section on Downtime has been expanded from the core set. Now DMs can get more out of buying/selling magic items, carousing, crafting and so on in the form of Complications. Good stuff!
Magic Items? Yes sir. The DMG has many uncommon and rare items but it lacks every day magic. The Guide introduces a slew of new common magic items including a Greyhawk themed one, Heward's Handy Spice Pouch. This wondrous item does exactly what you think it does, nothing extra fancy ;)
There are some spells in the Guide too. First on the list in fact is Abi-Dalzim's Horrid Wilting, a classic from 2E Tome of Magic. You may ask why I mention this spell? I personally co-opted Abi-Dalzim into Greyhawk after I noticed the named mages in toM had no backstory. Dalzim himself haunts the Ulsprue Mountains in Ull. You're welcome.
Another classic, Melf's Minute Meteors also returns for 5E. Then there is the 8th level Mighty Fortress spell which is just a temporary Daern's Instant Fortress I imagine.
Lastly, what spell list wouldn't be complete without Tenser's Transformation? Happy gaming everyone.
