1. Power levels and attention to detail are rather hit or miss here - too much of a disparity.
Dependency vs Insanity, for example.
2. The whole product seems less carefully thought out than previous playtests such as the oracle, summoner etc.
Flaws seemed to me to be hastily slapped together, and a much better job could have been done. A character's flaws can be at least as interesting as their advantages and paizo has taken a whiff at what could be an amazingly interesting and fun contribution to the game.
For example mythic clerics could gain a limitation to their spells that corresponded to their deity's domains.
A character could have spent 30 years polymorphed into a squirrel and so gained the ability to speak with squirrels but had rather unfortunate quirks regarding nuts.
While hubris is represented, lechery, gluttony, despair, unluck are not.
A lot of systems have done great flaws systems: gurps, hero. Do something interesting.
3. I know I'm preaching against canon - but what does the stricture about "types" gain you? How does the imposition of "archmage" or "hierophant" add to play.
Why not simply arrange powers into disciplines. Make the requirement that a player must select three minor disciplines before they can select a major discipline - and then make all the powers open to all.
Much more interesting combinations that way.
4. Disadvantage of archetype: Whatever the perceived advantages, mythic abilities were shoehorned into whatever archetype you came out with. Additionally the choice or mythic archetypes changes the focus away from your already existing character classes.
For example - there is relatively little love for druids, oracles, monks. No doubt that you will come out with additional archetypes- but you will never have as good a fit as if you either allowed free choice by the players or class bassed archetypes.
For example: Movement abilities get much less love than combat abilities.
Shapechange could have been a huge advantage: Give people the ability to change into different creatures. Allow them to gain supernatural abilities. Allow them to pick 1,2, or three additional attributes. Let them apply templates. (Although I suspect we will eventually see a mythic shapechanger).
Items could have their own discipline: Some mythic characters could handle cursed items: perhaps one minor discipline would allow you to remove them from anyone. Another would make any crafting failure become a cursed item. Perhaps a major discipline would allow a user a list of qualities that the user could add to wondrous items like we currently do to with weapons....
So I love the idea of a mythic expansion. I love the idea of mythic challenges. Both these are solid rule frameworks. But the archetypes and the flaws systems flunk.