Warhammer 6th Edition will no longer include the flying high rule. Flyers can now only "swoop" 20 inches and are considered to be landed at the end of movement. Personally, while some might disagree I think this would be a good change to see. Flying high has been the source of a number of arguments in the past (in my experience anyway), and it would make flying units a lot less "beardy" and more like ultra-fast cavalry.
"Overun" may occur when a charging unit entirely destroys their target. They may follow up and charge a new unit that same turn, rolling dice to determine distance.
Chariots do d6 impact hits as before. Most chariots however strike at St. 5 now rather then St. 7 and scythes wheels only gives them +1 hit to the d6 roll.
If a Fast Cavalry unit rallied at the beginning of their turn, they may move normally that turn instead of staying put as other units have to.
I've also heard mention of "stubborn" troops which will take leadership tests unmodified. Expect Dwarves to have a number of them then.