I usually prefer not to add any additional material to the basic rules of a game and very rarely use 3rd party material, but I really like The Secrets of the Oracles.
It's 6 mysteries, 6 curses, and 6 archetypes. That's what you pay for and that's what you get. There are no additional pages dealing with making oracle characters or how to implement them into a campaign.
Regarding the power level, nothing appears to be exceptionally good, but at the same time pretty much everything seems to be an actually viable option that can work out well for the character. Something that I usually don't see often in d20 splatbooks, except for the Pathfinder Advanced Players Guide, which brought us the oracle in the first place. Usually it's two or three gems in a book of forgettable stuff, but here everything is actually useful.
The mysteries and curses have me completely convinced, but the archetypes are actually getting a bit too far, almost completely replacing mystery spell lists and relevations at lower levels and even at higher level your archetype will be your primary mystery, withyour actual mystery affecting only the list of relevations you can chose from after you got those from your archetype. However, the Ascetic and Mad Prophet are still very interesting choices, and the Tribal Shaman and Wanderer could also find some fans.
Among the curses, only Technical Ineptitude seems a bit too situational in its benefits, but the others are all interesting blends of drawbacks and thematically fitting benefits.
I think there's a focus on more "savage" campaigns instead of urban ones, with the Rot and Primeval mysteries and the ascetic, crone, tribal shaman, and wanderer archetypes. The Arcana, Darkness, Luck, and Sound (which could also have been called Voice) mysteries should be useful in an urban setting as well, however, and the curses can work everywhere.
If you play a campaign in which oracles represent a major spellcasting class, and is maybe even set in a wilderness setting, I actually recommend getting it, even if you are not looking for additional character options. The Secrets of the Oracles not only provides those, but also adds new elements to the game world as well.
[5 of 5 Stars!]