thanks to new animations
new weapon tiers
new skins
scavenger mode
realism mode
new achievements
difibrillators
pre order baseball bat and halloween demo
Campaign's time of day/night differ each time played thanks to director 2.0
multiple pathways thanks to director 2.0
a mall-related campaign
"boomer bile bombs"
honking clown zombie noses
grenade launcher
"speed boosting effects of adrenaline"
"deploying ammo upgrades"
a burst-fire rifle (not that anyone uses the rifles)
"forming teams"
The chargers ability to push survivors over 80ft
Chainsaw abundancy (judging from the achievement to kill 100 infected with one)
etc.

and Zombieland was damn good.
Fun Fact: my latest picture has been half-finished since August