Yū Yū Hakusho's "Three Kings Saga" catches a lot of flack from fans of the series. Most of this has to do with the way everything played out; it's rushed, the stakes don't feel all that high and neither the action nor the emotional moments are done much better than anything before it. For the last major arc meant to wrap everything up, it's disappointingly lackluster. It seemed as if Yoshihiro Togashi, for all his brilliant story writing, really tripped hard at the finish line.
However, just because the arc didn't meet fan expectations doesn't make it bad. There was still a lot of good to come out of this story arc. In addition to its new settings and characters, it further developed the series' protagonists. As far as concluding the story is concerned, this was a decent way to go about it.
A common point of contention for this arc was the Demon World Tournament. To many, it seemed underwhelming and repetitive when compared to the Dark Tournament, but this is a bad way of looking at this plot point. As far as tournament arcs in Shōnen Jump go, this one played out fairly uniquely. The protagonists lost to both primary and minor antagonists and the winner was a complete dark horse. The fact that the stakes aren't life-or-death like in the Dark Tournament meant they could get away with developments like this. Having all these factions that have been feuding for ages settle their differences with a tournament may not be the strategic mind game fans were promised, but it was fun.
One of the best parts of this arc is the expansion of the Demon World's lore and inhabitants. In the previous arc of the series, the "Chapter Black" Saga, Sensui's true goal was revealed to be getting to this mysterious plane of existence however he could. Sensui's methods were questionable but not unfounded. The desire to see the Demon World is a sentiment shared by fans of the series.
Prior to the "Three Kings" Saga, the Demon World was a large unknown of the series. The only glimpse of it fans got to see was during the "Spirit Detective" Saga when Yūsuke and his friends went to Demon City to stop the Saint Beasts. Even then, most of their time was spent in Maze Castle, so there wasn't really time to explore the Demon World.
The "Three Kings" Saga gave fans a much better look at the Demon World. Sure there are castles, but there are also icy mountains, forests, plains, laboratories, and more. There's a sort of beauty to seeing all these different kinds of settings paired with the Demon World's signature dark thunderclouds; it really makes the Demon World feel more like a "world."
It was also interesting to see more of the Demon World's inhabitants. Prior to this arc, most demons were made out to be monsters who could only think in terms of death and destruction. Even the more humanoid demons like Koto and Kurama had a savage side. These aspects still existed in the newly-introduced demons, but now there were also more civilized, more intellectual, and even more sympathetic demons. Again, these nuances made the Demon World feel much bigger and more alive.
The main characters also get great individual story arcs. In particular, Yūsuke, Kurama, and Hiei all get more information on their backstories that helped each of them grow as people; Yūsuke's demon heritage was debatable because it's seemingly pulled out of thin air with no setup, but Togashi followed through on it nicely. Kurama's struggle to find a happy medium between his new human and demon self was also engaging. Hiei's backstory and the connection he formed with Mukuro were both real treats for the fans. It's amazing how after all these characters had been through, they still had so much room for personal growth.
However one feels about this final arc, it was a good conclusion. It wrapped up so many of the series' major character arcs and plotlines that the story truly feels complete. This might not be the best possible sendoff to the series, but what it gets right, it does really well.
