The story was already good when I started watching the anime, before reading the manga, but after the anime ended there were many unanswered questions, after start reading the manga at the middle part, I noticed that there were some minor changes in the anime, though this, the story wasn't very altered from its predictable ending. By the manga itself, it's a great shounen-style story, with the usual quotes: "I never going to give up on my dream!" and "You never going defeat me!"; the main character tries to befriend with everyone he meet, though some of them have a nasty personalities, but when they met someone who is really bad they don't think twice in defeating him/her (quite different from Rave Master hero, who forgives even the main enemy); the comedy parts make its way through the chapters as a "cooler" from the action arcs, well placed actually; the only thing I can actually complain about is that 98%(I believe) of the chapters there is always someone crying, whatever is the reason.
Zatch Bell worth the reading, waht else can I say? But you can always watch the anime first, just keep in mind that is not completed.