The summary should give it away. Shaman King (2021) tries to adapt the original, complete story of the Manga with the same name in even less episodes than the original anime adaptation from 2001, which had an already pretty rushed alternative ending (due to the fact the manga was still on-going).

For roughly the first 20 episodes both anime adaptations are almost identical and it has really been nostalgic to me to re-watch a visually enhanced version of the same story I watched almost 20 years ago on kids-TV. While Shaman King (2021) looks quite good, staying true to the original adaptation while using newest technology, the fight scenes, the heart of any battle-shounen anime, are beyond bland. They barely even hold up to the 20 year old fight scenes in Shaman King (2001) and have a lot of stills and images with little movement. I never remembered Shaman King for awe-inspiring images or mind-blowing fights and neither expected any of this, but the new adaptation had fights so boring, I thought about skipping them.

Once Shaman King (2021) splits from the original anime, to finish the story of the manga, it really declined quickly, throwing new characters at the viewer in every episode, jumping through several arcs of possible plot points in sometimes as little as one episodes, killing off side characters as fast as new ones are introduced. At the end the plot becomes such a mess I didn't bother enough to keep track any more and just wanted it to end.

Aside from the abysmal and rushed story-telling Shaman King also suffers from the typical shounen anime problems. We have a MC, who mostly only beats down foes before letting them leave, despite them repeatedly trying to kill him or his friends. Normally this wouldn't be much of an issue, because important characters seem to never be in any mortal danger in shounen anime anyways - and I don't remember that I has been a big issue in the 2001 adaptation - but Shaman King (2021) is actually quite brutal in that regard, killing off characters left and right. In Shaman King (2021) characters get blinded, maimed or killed with most of the main characters still neither being serious nor apprehending the villains in any way.

This is all topped by Conchi and Ponchi, probably the worst animated characters since Jar Jar Bings. They are lound, annoying and fight mostly with their testicles. That's right these 2 animal ghosts have extendable balls, which they use to violently shove them their opponents - and the viewer - in the face on every possible occasion. These 2 are so unpleasant, that I can understand anyone dropping the anime just because of them.

Final Verdict: If you want to watch Shaman King, watch the 2001 version, which even though not featuring the original ending, still has a better plot than this hot pile of garbage.