Don't quite like: The "Few rules, lots of exceptions" approach. Few, simple rules to handle every situation is ok, makes the game go smooth without looking to the PHB/DMG/MM/MMII/MMVIII/Complete x/Whatever every 2 minutes, but the "lots of exception" part scares me... ok, there are lots of ways to circumvent this (Power Cards, to name one), but it still scares me...
Don't like: Sorcerers, Druids and Barbarians out of PHBI... I have a (BIG) place for them in my Work-in-Progress setting and now I have to wait for PHBII, denying my players some character options for months.
Fear: Lots 'n lots of character options, powers, feats, paragon/epic paths that will make character creation an epic quest by itself.
Even worse fear: Lots 'n lots of character options, but some build/combos so blatantly overpowered that character creation is going to be one-way.
Fear: Combat length won't be any shorter than it was in 3E.
Fear: 50+ classes...
Various fears shared by others, mainly:
- Marks, lasting effects and such annoying to manage.
- Automaton combat behaviour of character.
Absolute uber-fear: My group won't like 4E (and in that case I would have "wasted" months in world building and I would get really sad)