Yeah, it was an ancient manga that I suppose wasn't able to be made into an anime until recently. I enjoyed the anime, I did; but I personally was let down by not only the direction the show went, but also the lack of a satisfying conclusion. For the longest time, the show built this hype around Shinchi and his abilities; I really thought there was going to be this awesome final battle that displayed how bad-ass he was - in the end we didn't get anything close to this.
*spoillers?* Take, for example, the final episode; I can't remember his name, but that crazy guy held a knife to Shinichi's woman, and Shinchi finally admitted he wasn't just a regular person - right here is where I thought they were going to make him use his super speed (something made apparent earlier) to save the girl. They didn't, though; they made Migi save her, and then the show just ends, and I felt really underwhelmed by it all. I mean, the final monologue was nice and only a fool would say otherwise, but I still can't feel the conclusion could have been far grander than what it turned out to be, even if it risked straying a bit from the original manga ending.