i fully intended to try the game out again if Sega offered a free month trial, but after running through the screenshots, i'm not even going to bother. There's some nice changes here, but it looks to be too much of the same. Again.
Changes according to PSO World:
# Remappable keyboard buttons for action palette on your lower screen (extended, you can map techniques and actions to keys 1-0)
# Server side saving to preserve character data
# Game masters to establish order to communities
# Staff characters
# Is an X-Box port
# Control improvement involving keyboard and mouse
# Native high resolution mode
# Better textures
# Existing characters will look better (same existing 12 classes, no new additions)
# Higher polygon count
# New NPC's introducing new adventures (not on Gamecube or X-Box)
# New team system will let you register teams with the server and be known by that team which will enable you to create mini communities. Once you have a team made, you have your own real time chat channel that runs independently of what ship/game you are in.
# A completely new map and new set of monsters.
Edit: The above taken from
http://www.planetdreamcast.com/psoworld/psopc.php, which got their info from the Japanese version of PSO BB.