I'm looking for a series where you can see the author's art improve as the series goes on. I just think it's really neat to see where they started and how they end. A couple examples are Hatenkou Yuugi and Immortal Rain. Thanks!
Alive - The Final Evolution art wasn't pretty (at all) at the beginning. Made marked/huge improvements compared to first volume release. Looks less amateurish and more pro shounen-like style as time went on.