I expected big things from Shaman King. The manga author was originally Oda's assisant who is doing One Piece, who was also an assistant to Watsuki, the creator of Rurouni Kenshin. With influences from manga authors who have drawn two of the greatest shounen mangas ever, you'd expect Shaman King to be at least above average. Well, it was average at best, and there's really nothing good about that. Shaman King excels in its rich world and fighting concepts along with producing some pretty cool characters, but terribly lacks in its weaker areas.
A shaman is someone who can see the souls that remain unrested and roam around the earth. The shamans are able to bind with these souls and absorb the powers and techniques that those souls previously had. When I mean powers and techniques, I'm talking about the generic shounen variety, such as flying hydras, skeletons, and beams (in fact, one character's attack is simply named "beam"). These guys are usually invited to a tournament to compete for the title of Shaman King who is granted great powers. Yoh competes in this tournament in order to achieve eternal relaxation. Throughout his journey, he meets other shamans and unite with them in order to overcome the evil that is brewing behind the scenes, along with competing for the title of Shaman King in order to fulfill their own individual dreams. Yoh is a bit unique in his own sense. A guy with great work ethic who strives to become stronger to the point where he can slack off for the rest of his life? New to me. However, the problem with Yoh is that he's a bit too superficial. Anna, Yoh's fiancee, and Hao, Yoh's arch rival, also suffer the same illness of over sophistication. Anna is much too unpredictable in a bad way. She'll be way too strict, way too calm, and way too demanding all at the same time! Hao is a bit one dimensional; predictable behaviour, his hobbies are laughing and smiling sadistically, and his character really doesn't develop until the last two episodes.
Though Hao isn't the only character that lacks development. This show really doesn't have a lot of character development at all! Most of the characters stay the same. Conflict is pretty vital to any story, but none of them any more important than character conflict, which is where Shaman King greatly lacks in. Though it is all a matter of preferential taste, because Ryu and Chocolove, two members of Yoh's group, really don't change, but are extremely likeable characters.
The characters are tolerable, because you'll find one or two characters you'll like, but the filler makes this anime borderline unbearable to watch sometimes. A couple of fillers would have been nice, but the middle portion of Shaman King is just abundant in filler that is both uncreative and plain boring to watch. You'll find a couple that are rather exceptional, but there are much more bad filler out there that is quite unforgiving.
When you start getting out of the filler phase, you run into a tedious process of good guy meets bad, bad guy is on the verge of winning, and then good guy pulls off some miracle win completely out of his ass. These bad guys also become good and aid the good guys in their journey to defeat evil. Follows the shounen guidelines perfectly. Even worse is that the ending absolutely sucks. Deus ex mechanica at its very finest.
Shaman King fails as a story in general. Fortunately it is also a shounen anime, and there are certain elements to a shounen anime that attract people, like me, into watching them. Tournaments, strategical battling, suspense, training, it's all here...in a watered down fashion. Yoh does some rigorous training exercises in the beginning, and almost never trains again. In fact, almost none of the other characters go through a process of training, yet they somehow get stronger. In fact, there's a sequence somewhere in the anime where the characters literally gain an immense amount of strength within the span of a second. The fights are pretty strategical and sometimes entertaining to watch, but they're severely dragged down by the usual "What you're doing is bad" speech, in which they will usually turn good after being defeated.
Shaman King reminds me of another middle of the pack shounen called Rave Master. Rave Master suffers from trying to be too badass and cool, while Shaman King suffers from trying to be way too unique and different. The difference is that Rave Master was much better presented and got consistently better as it went along. Shaman King would have these spurts of goodness followed by some long periods of suckiness. Only true shounen fans would possibly enjoy Shaman King, though if you have other priorities in your list of "what shounen to watch next", Shaman King should be at the bottom.