The 2.0.x series of Geotools represents a major restructuring and improvement over the 1.0 series of Geotools.
This series has now been retired, with the last stable release from this branch being 2.0.0.
GeoTools 2.0 At A Glance
This release featured all manner of improvements over GeoTools 1.0, and represents the community aligning itself with open standards. A major component of this effort was refactoring the code base into a new modular structure, as desribed here.
The original developers guide is available: