Unlike many others, I didn't mind the "slow" start. I place an emphasis on character depth, and I didn't find the first parts boring at all because of the time taken to draw a good, realistic portrait of the characters, complete with little idiosyncrasies aplenty.
And then when the plot, intrigue, and action take off--it becomes an explosive and compelling ride. If you're set on the typical shounen plot lines of training, power-ups, and progressive battling build-ups, this probably isn't for you. I enjoy the insertion of realism into this supernatural setting, however strange that may sound. You won't see magical weapons, godly techniques, or wise masters popping up before every major fight to impart some new power to the protagonists. It's mostly sweat, hard work, perseverance, and trial-and-error.
Love the tidbits of romance that don't take over the kickass battle art and political tug-of-wars!
Ok, and yeah, I love love love all the random monster design 8D At least I saved the shallowest reason for last, right 😕