I would put this series on par with He Who Fights with Monsters & Defiance of the Fall.
The story of how they enter the Infinite Realm is something truly grand & very well written as it ties & plays a role through the entire series to date.
The characters are astounding
The power system is very flushed out varied and interesting.
Seriously, the best thing I can say is I enjoy this series as much as the other two listed & that is the highest praise I can give it.