To properly criticize Shaman King, I want you to understand that Shaman King came out from an era where shounens were the determined bread winner, and there were plenty of attempts of random shounen being released. At the same time, things like Naruto, Inuyasha, Hajime no Ippo and Hunter x Hunter were airing or finished airing and plenty of other commercial shounens were being released or about to start in that craze. I wouldn't call Shaman King succesful, as the way I have stumbled upon it I consider bizarre.
It started airing at 10 PM on a cartoon channel. What's bizarre about this is that it and Naruto, are the only two anime, that ever did that in my country. Naruto, understandably was a cashcow, it makes sense, but Shaman King was the experiment before it. No knowledge of it being an anime, aired quite late at night, signifying that it is intended to older audiences, and it did well. I stayed up every night to watch it and talked to friends about it and we enjoyed it. Outside of Dragon Ball and Yu-Gi-Oh, which aired on some random completely different channels, for most of the kids I knew, this was our first shounen experience, at an age where we could actually understand it. I expect that Shaman King was a cheap bargain for the audience my country tried to hit with it, and that it worked out quite well. Because Shaman King was really enjoyable and really enjoyed.
The reasons it was enjoyable for are that there finally was a cartoon that tried to define the characters as persons, and explain their state. It also kept all the familiar traits of other cartoons that we were seeing, which were in its humor, and had themes that weren't really explored here, but worked in other countries for their young audiences. No cartoon that I've watched at that point really attempted to create character development, or any overarching plot, and instead were mostly one offs. Shaman King did do that, maybe not that a level that I would consider commendable today, but it did do it. It was comedic, but it played off based on the personality of the characters, and also how they changed. Their actions did matter past the scope of the episode, and that really won me over. The fact that the world can get more complex, the characters can evolve, and the fact that story was going somewhere. There were pretty few examples of other shows that even managed to do an attempt at this at the time for me.
But its problem today is a simple one. Due to the competitive scene at the time, Shaman King falls short to almost every show, and pretty much any modern show, can easily outclass it. I mean, it had poor production values, with each fight having some still frames and barely enough contact was ever done between characters. Most of the budget was spent on making sure the designs and characters are consistently colorful and have enough details, but there really isn't any fighting choreography, which is a detriment of the series, and in action scenes the characters may sometimes look remarkably choppy. The story doesn't really have a pace or a clear structure, so that might mislead a lot of people into drawing conclusions about the series, which won't work in its favor, due to how laidback the attitude of its characters can be, or how many liberties it will take in its structure. It is filled with character archetypes and tropes that are across most shounen anime. And its overall theme is the power of friendship. Based on what I enjoy now, I can say for certain that if I came across Shaman King today, I would not care much for it and think it was bad. The factors that made it good at the time are that everything else didn't really have any sort of direction, when Shaman King did and I didn't really have a lot of the criterias of comparison I have to other shows now, that making Shaman King pure novelty to me.
This doesn't make Shaman King necesarily bad, it just means that it is hard for someone to determine whether they would like it or not, and that it is hard for it to get any sort of notoriety when there's far better looking options, and the fact that it is a shounen might turn off a lot of people because it is one. I personally don't consider it bad. While I think most of the fights were dull and uninteresting, with a few exceptions, what has driven the fights was the dialogue and the progression they went towards. The actual fight itself for me being dull was easy to overlook based on the fact that Shaman King knew how to properly state why what was on screen was happening, what was the goal, and where the character has to get to win. The quality of the fights in Shaman King will vary. Sometimes they can be really interesting, like a certain fight where someone led the main character into discovering a new power, and sometimes they can be really dull, which is when the characters simply win by showing their powers and doing some movements in order to meet the quota of "this is an action shounen".
I wouldn't honestly call Shaman King an action shounen as much as I would call it Final Fantasy XV. A group of guys, travelling around, getting powers, and enjoying off the road they are on is what I mean. It is often comedic and playing off the personalities of the characters, but it can also be serious whenever there's a "protecting my friends, family, morals, ideals etc" type of shounen shtick to be presented. It can be mature and well executed when the situation calls for it, but it can take its time with comedic moments insignificant for the overarching plot or simply go in a serious direction out of nowhere. Due to Shaman King bouncing too much between where it is going and where it wants to go, it can sometimes seem slice of lifey, and this made its overall pace to suffer, as the stakes were constantly being toyed with, and as a result of this, where Shaman King was moving towards wasn't 100% certain at all times. I know this is an odd thing to say when the series is titled Shaman King, in a series about people fighting each other to become Shaman King, but the story takes a lot of random detours or restructuring of how it goes about things, while mostly keeping the reward of being the Shaman King as ambiguous and potentially anything, this leading to an odd type of progression in the story, where you didn't know what the stakes were, until Hao happens.
Unfortunately, the execution of the villain, Hao, is not particularly good, as he is defeated through the power of friendship and he is portrayed as a generic edgy cartoon villain. So the series doesn't really benefit too much from having him as a villain as much outside of him being just a reason for the characters to become more serious. This villain is pretty much where Shaman King becomes a chore to suggest anyone to go through with it, since he becomes an important part of the anime, his manga counterpart is a lot more human and developed, and this counterpart doesn't really have any traits that make him that. He is a threat for the sake of being a threat. He doesn't completely weaken the series' high points, but since he's the focus, Shaman King becomes less entertaining as he becomes more and more prominent. Which doesn't really make me sell Shaman King in terms of the story, despite of having various elements well executed, and well implemented humor that plays off various character traits very well.
But still, my view of them today, with my view of them back then, isn't exactly in sync. For instance, the introduction of a major character in the series astonished me due to the fact that this was the first time I ever saw a guy being introduced by chopping a car in fucking half for absolutely no fucking reason out of nowhere. Today, the same scenes of him made me laugh my ass off, because of the fact that he gave me the impression of an edgy little troglodite upset at the fact that his parents never bought him Hot Wheels ™. The fact that he afterwards rants about he is a superior being while looking at some cars in traffic strengthened that remark. I might be more fond of the characters due to the fact that I've experienced them while being young, but I still think their personalities were executed quite well and that their motivations are quite understandable. In addition to that, the personalities they have play off each other well. While I don't think they singlehandedly are unique characters or have any particularly unique character arcs compared to other shounens, I do think they are executed well due to the fact they are simple. Partially is due to the adaptation not really adapting some of the parts that gave more depth to some characters, as the anime focuses more on making it a truer shounen.
I can't really recommend Shaman King on any other basis than curiosity. It is a story about some kids going through a tournament to become God and fighting each other with not particularly well done animation. The themes it has are common and you've probably seen something else similar to it at this point you would draw comparisons too. The only real praise I can give Shaman King is that in smaller circles, in places where its main competitors were gone, it could stand out. It managed to be a shounen and if you seek that, as long as you don't expect much in terms of fight scenes, it can do the work quite well. But note, it doesn't have any lasting impact or build anything unique of its own. It just executes the aspects of a shounen to a decent level.
