The effort put into this tome is impressive! This will introduce additional mechanics to learn, however, much of it focuses on documenting your progress and integrating it into the system to further your adventure. What I particularly appreciate is its modularity in the varients section—you can use the parts that suit you and simply skip what doesn’t. I would encourage using all the base system at least, with variants used later for a custom experience.
Personally, I’m very pleased with this product. It works seamlessly with simple systems like Mörk Borg and more complex ones like Shadowrun 3rd Edition. You can use it for any decision-making scenario—whether that’s with other players and no GM, solo play, or even simulating a GM running "virtual" players. One area for improvement would be more guidance on adapting pre-written adventures for use with Mythic. I understand, though, that this is a nuanced challenge to tackle. All in all, great job!