Here's a better summary than the podcast Dagok:

# Melee weapons: chainsaw, axe, bat, frying pan. Judging from the videos the primary swing is slow but brutal, but you can still normal-melee to shove zombies off.
# New (reskinned?) firearms.
# Sunlight.
# Incendiary Rounds. Ammo stash powerup that gives you one clip of bullets that sets anything you shoot on fire.
# New special infected join the cast of old ones. Only one known so far is the Charger, which is a cross between the Tank and a regular infected. Can shouldercharge you with his one beefy arm, but will only knock you around, not incap you. If you go one-on-one, apparently he will thrash you until your face looks like hamburger unless you're rescued.
# Wandering Witches. Witches will now walk around so crowning is the best option rather than avoidance and a later, unexpected encounter.
# More varied regular infected. On top of just new models there are also hazmat zombies that are like regular infected but immune to molotovs/incendiary rounds. Also regular infected can now be dimembered to some degree.
# 5 new campaigns to tell the story of the four new survivors, from Savannah all the way to New Orleans.
# Improved Director. The director will now also manipulate maps depending on how well/poorly you are doing and change pathing options to make it easier or more difficult.
# Panic events are now Gauntlet events. No more waiting out a timer or meleeing a horde away. Level-progressing panic events will now only end when you reach a later trigger so closet-camping is out.

I'm just presenting the information, I'm still in the not buying crowd.