For me,
1. Removal of the Christmas Tree Syndrome
2. Balance at higher levels between spellcasters and non-spellcasters
3. Action Points are core
4. At least some undead will be critable (already a houserule in my 3.x game)
5. The possibility that class structure may work more like d20 Modern or Star Wars:SAGA
6. Wizard implements
Unfortunately, I still have to wait and see how 1,2,5, and 6 above are implemented. Beyond the six things above, I have actually been disappointed by most everyting else that has been revelaed to date. Yet, there is still time for WOTC to win me over.