Well, I haven't been able to get ahold of any yet boxes yet, but I looked through a spoiler for Champion of Black Magic the other day and was stunned. The set is amazing. There hasn't been a set quite so superb since Struggle of Chaos.
First of all, one of the things that makes a great set is good commons. Champion of Black Magic has these. Second of all, a good set will bring new decks into the environment. Champion of Black Magic does this. Last of all, a good set will make new uses for old cards. Champion of Black Magic succeeds in all 3 of these areas.
However, I'm going to discuss these out of order, because it simply works better that way.
Champion of Black Magic introduces 2 new deck types: Magicians decks and Amazoness decks. These decks are very, very good strong, and they will be feared contenders in the new Japanese environment.
Let's discuss Magicians first. These cards bring a new concept into the game: Magic Tokens. Magic Tokens come into play on certain cards, are added at certain times, and can ultimately be spent to do amazing, terrible things.
This is a fairly vague explanation, so let's beef it up with a good example. 303-015: Magical Marionette gets a Magic Token every time your opponent activates a Magic card. Not only do each of these Tokens increase his attack strength by 200, but you can remove 2 Tokens from him to destroy any monster on the field. Yowza!
Of course, there are also cards that support other cards with Magic Tokens. Some cards will allow you to add extra Tokens to monsters, and some allow you to spend any and all of your Tokens to perform devastating effects, such as destroying all of your opponent's cards on the field. Also, many Magicians have abilities that help you get ahold of Magic cards.