I cannot recommend this book enough! I discovered this series a few years ago, and have loved it since. :). This series has nearly everything- comedy, adventure, romance(in later volumes), and fantasy. It even has mecha, and a cute mascot. Plus, the artwork is amazing. :). It has to be my all time favorite CLAMP title, and has to be one of their best, art wise, as well. If you haven't read this yet, go out and buy it now. You will not regret it!
However, avoid the right-to-left formatted one. The re-writer of the series isn't as good as the one for this version, and many of the characters personalities are changed because of this. For example, at one point, Hikaru(the protagonist) comments on being able to see a baby in some house's window from the Tokyo tower. In the 'revised' edition, the exact quote is "Look at that fat baby in the window over there!" (I believe). This changes the statement from a simple comment, to a rude remark.
They also made the characters use 'hip' slang which was not in the first version. Or, more than likely, in the original. Avoid at all costs. ( )