What are the differences between Dark Days Ahead and Whales's original game?
DDA has more buildings, a few new critters, additional layouts for existing buildings (Labs are much nastier now), and generally just More Stuff.
That said, not all of it is "better". Places like the Office Tower, etc are well-designed BUT can have more hostiles than rewards. CBMs are no longer in multi-pack canisters--thus, somewhat more common--BUT strictly one specific bionic per unit. Vehicles are everywhere in-town, but most of them aren't operable.
And they fixed the ability to cook rotten stuff and have it come out fresh & nutritious.
That said, I'm playing a fairly recent build, so it's a net gain--but if you're coming from the Whales build, you may have a nontrivial learning curve.