So far I have only read Tsubasa: Reservoir Chronicles and X/1999, but I am in love with Clamp's art style. Gorgeous flowing lines, intricate backgrounds and compositions, unique and instantly recognisable character style. I only wish I could one day produce something so beautiful...
Doubling is a theme which crops up again and again. I always find works dealing with this subject interesting.
I have heard that there is quite a lot of diversity in the style of Clamps different works, so I want to read more of their manga series to compare them. I have also read that the clamp artists are largely self taught, which gives me hope for the future!