Since I posted these on DE's blog, I figured I might as well copy them here for people who might actually care. These are most of the concepts that are going into the new version of PC, some of them are already done, most of them are barely started, some of them will probably never happen.

- Looting zombies/stores for clothing to customize your appearance. You'll be able to get any clothing item you've previously found from any dresser-like object placed around the world. There will also be laundromats, since if you loot clothes from a corpse they'll be all bloody and increase detection range.
- No true "health", your status drops from taking damage, but also from long periods of activity. You have to sleep, eat, or use a restroom to recover it. You won't be able to move while using these, so its best to find a safe place first. And sleeping will completely blank the screen.
- The zombie AI in the new PC is somewhat mindless, you can freely walk through the horde as long as you don't get too close (which is actually pretty difficult). Same as with yours, a gunshot will pull the entire horde onto the player, though mine go directly for the player, instead of investigating the area. I like your idea better as far as that goes =P
- Modifying weapons, instead of magically leveling/upgrading them. You will have to find sights, mags, grips, silencers, etc. Instead of just talking to some guy for an upgrade. These will also visually effect weapons.
- The HUD/Inventory systems in the new PC works somewhat like an FPS game. You can only carry 9 items at a time, and each number on the keyboard relates to one of them.
- Ammo will be a lot scarcer, though not impossible to find. It will take up an inventory slot, so you'll most likely only want one or two weapons at a time, instead of trying to max them all and carry each for the default ammo.
- The shooting mechanics work like a dumbed down version of Alien Swarm's. Instead of just holding F and auto shooting at everything, you actually have to somewhat aim and click. And you move with WASD so it feels/plays more like an actual shooter/game.
- Moving barricades will be done in a more Zelda-esq style. Holding down a key to drag them around, instead of just humping into them.
- There will be several human factions around the city. They will drive the story/quests - something like FONV, but less horribly designed.
- I would also like to make the map about 4x is current size, and actually fill the entire thing, but I doubt that's going to happen.
- Along with that idea I'd like to have it where you can barricade off entire city blocks to live in for a while.
- I also have a possible sewer system planned, where you can dig around and make your own paths under the city (safer from zombies), but I doubt that will happen either. This would tie in to power/water/gas grids.
- Forming groups of AI to travel with you, and those AI having dynamically generic personalities.
- And a custom building system, with fully destroyable houses which need to be guarded/maintained, but provide a safe-haven that you can send your allies to.
- Melee weapons and dual wielding will both be possible. Though I'm not sure about dual wielding melee weapons...
- Special infected. L4D style and BeYOND!
- Maybe some other things?

EDIT: That was just a list of new additions/changes. Here's a quick list of things that have been removed: Squads, Classes/Skills (skills will probably be reimplemented in a new way), Nightly Raids, Drones (temporarily), Transport Tab, ???