This, simply put, is one of the best anime series I have ever seen.
Without revealing too much, the basic plot line of the show is about a self-proclaimed mad scientist who accidentally discovers time travel. The show focuses on his attempts to change the past and the future, and explores the resulting effects on the physical world, relationships with those around him, and his own mental stability.
This is an incredible anime and if you are a fan of the series, are slightly interested in anime, or have no interest in anime at all, you should buy this. It is a great show with an interesting premise and strong characters.
At the time of writing this it is also the cheapest price I have seen for the whole series. This DVD set contains all the episodes of the series with a few extras and the OVA. Do yourself a favour and get this show!