basically, it's just a really poor adaptation of the manga. as the manga wasn't finished at the time the anime was made, it made up its own anime-only ending - which isn't uncommon, and is usually fine. however, they went totally off the rails and made up a bizarre subplot about witches and magic and stuff, which strongly goes against the theme of the series (the ability of normal people to do incredible things.) on top of that, it actually completely changes the manga plot from episode 1. in the manga, the murder of yako's dad is solved within the first few chapters; in the anime, it's the overarching mystery of the series, which doesn't work out that well, considering how stupid the ending they made up turned out.

it also thoroughly ruins the characterization of the lead character, yako, by making her into a pretty wishy-washy "chosen one" type character instead of the feisty and innovative high school girl, and cuts out some other interesting characters. and, in general, it just lacks a lot of the charm and wit that matsui's writing had. even though the manga is longer and the art is dodgy, you're much better off reading that instead.