This show is great! The setting takes place in an apocalyptic future where Robotnik is the head of the oppressive government and Sonic and his siblings Manic and Sonia fight for freedom. They came up with some interesting show elements for this, like the alternate universes, other cultures, experiments, oracles, and people in danger. Sleet the wolf/dog was a cool character.
SU had excellent animation, but it did take place in a dingy city, so that might have lessened the impact. I liked the music-video songs that they sang; some were good. All the intrigue of the hedgehogs trying to find their mother the queen, Sonia getting mixed up in Robotnik's politics because of her friend Bartleby, the character humor, nice music and sound effects, and the variety of settings and plots makes this one of the best cartoons I've seen! This was my favorite show when it aired. I have seen pretty much all the episodes. However, it was a little repetitive sometimes with the constant escape from SWAT bots and Sonic's constant mentioning of chili dogs. Sonic Underground is much better than this new Sonic X series, which has slower, less interesting plots.
