The manga, I felt, became quite dry and insipid during the end of its life-cycle; it became too arbitrary and lost focus, yet continued to exhibit potential that wasn't harnessed. Personally, I was more satisfied with the anime due to the fact that it felt less protracted than the latter stages of the manga. I would be intrigued if some of the later stages of the manga were animated, but I don't think the rest of the series would warrant such treatment.
In earnest, I think the Naruto manga is showing some pains that the Shaman King manga began to suffer later in its life, but I recognise that Naruto's foundation was more firmly established than Shaman King's, giving the series more room to flourish.