This series plays on the expectations of the viewer, in quite a clever way. The bizarre opening sequence sets the stage: the audience knows that this isn't a normal anime series, and that anything can be expected. Then, there are a few "coincidences" that are given too much airtime to actually be coincidences. At least, that's what you start to think. You get to be hypersensitive for little details that might help you make sense of the plot.
However, making sense of the plot is an uphill battle. Shonen Bat attacks seemingly random people (starting with the designer of the popular Marumi mascot, young absent-minded Sagi Tsukiko), leaving them heavily wounded. His trademarks are the golden rollerblades and the dented, golden bat. Of course, a police investigation is immediately started, and as the number of cases start to pile up, the evidence just doesn't make sense.
Unless Shonen Bat is a psychic projection, a physical manifestation of the stress felt by people who have nowhere to run, who are trapped in reality. This opens the door for the 'middle episodes': a series of shared psychotic hallucinations (I especially liked the 'game-episode'), or simply rumor-mongering. Shonen Bat gains the status of an urban legend, and everyone knows someone who has been a victim of Shonen Bat. The phenomenon grows...
Until we come to the last few episodes, where we return to the cast of characters that we got to meet at the beginning of the series. Dark secrets are uncovered, and the mascot everyone loves turns out to play an important role... In the end, Tokyo gets saved by madmen, but it remains to be seen whether it will change anything in the long run.
The series is quite psychological, in an un-obtrusive way. We get a few fun rides in the dark recesses of the human mind. It's about as bizarre as, say, Serial Experiments: Lain, but more accessible. And it shares the dark, brooding and supernatural atmosphere with Boogiepop Phantom. I almost feel like the creators wanted to experiment with a different type of storytelling in anime, and they have succeeded admirably.
The designs are attractive and the animation is smooth -- visually, this series is a treat. The music is very nice as well: the ending theme, an understated melody on an organ is mostly used to accent certain scenes.
I recomment this series to anyone who enjoys a good mystery now and then. I'll give it a 8.5.