I've been talking about it here and there on Twitter, but I figured I would go ahead and compile everything I'm willing to say about Zombieville 2 right here. So without further ado...
The project began shortly after Battleheart's release, with the original intention being "let's update Zombieville USA with shiny new art." It's easy to see when you look at Battleheart right next to Zombieville that our art style has become a lot more refined over the last couple years, especially when it comes to visual effects like explosions, fire and other such stuff. A visual facelift, along with some modernizations like multi-tasking support were all that we originally planned.
It quickly became clear as we spelunked through our old project files that there was a lot more we could do. Wireless, co-op zombie slaying has been the most requested feature since Zombieville launched, and since we were tearing up the ground anyway, we started looking at how we could build the game to support multiplayer via iOS's Game Center.
The further we got into multiplayer, the more we realized how weapon variety could be expanded and improved. In Zombieville USA, there wasn't really much strategy to what weapon to use - you just steadily progressed towards the more powerful stuff, until you were basically spewing laser beams all over the screen at all times. Weaker weapons quickly became obsolete as you progressed. So we started redesigning the flow of the game to encourage a balanced use of different weaponry that each have strengths and weaknesses, rather than one weapon simply being "better" than the previous one. Weapons will vary in more than just damage - ammo capacity, mobility, area of effect, and control will all factor into your choices. Some new additions include stun grenades, landmines, sniper rifles and my personal fave, the "Cryo Gun" which encases its victims in ice.
All of the above led to the somewhat difficult decision to extend the gameplay from a single axis onto a 2.5d plane, similar to OMG Pirates or Battleheart. With two players romping about, it was simply too crowded to have the entire game take place in a single straight line anymore. The addition of depth added all kinds of possibilities in enemy and weapon design, and a new layer of player skill, since "aim" is actually somewhat necessary, and its now possible to run past zombies who are trying to box you in.
We also realized that adding a selection of different characters with pros and cons to Zombieville USA was one of our most beloved updates, so we decided to ramp this up to the max. In Zombieville 2, you'll find a large selection of character skins to choose from... we expect at least 20 for launch. Further, instead of them having "built-in" pros and cons, such as changes to movement speed, damage, ammo capacity etc, those benefits will be in the form of perks which you'll select yourself. So you'll be free to mix and match character skins with different bonuses that you prefer, rather than being roped into always playing the ninja if you prefer melee weapons, for example.
So to sum up: we basically started off with the intention of painting a house, but instead tore it down and are building a mansion on it. Hope that gives you an idea of what to expect when we release, which is expected to be sometime this summer.