The story is a lot like Zatch Bell (Gash Bell) in the beginning, then it sort of develops to a yu yu hakosho feel to it.

The Story is rather fast paced has there is not a lot of down time where the character goes off and trains to evolve in some way. I's mostly about fighting with special powers.

The Art was a bit awkward as the characters got more "attractive" as the series progressed.

Ueki is the the main character and always fights for what's right and sacrificing everything for his friends. This plays a role through out the entire series.

One thing that is often weird is that fact how Ai follows him around constantly trying to make sure Ueki doesn't disappear. It is brought up early as to why she cares so much about it but is is dismissed and not fully explained.

If you liked Gash Bell you fill like this it's pretty much the same path, only with different obstacles.

Anime follows that manga pretty conclusively not much deviation