It mixes it up, some chapters you'll be gunning/stealth killing a load of zombies whilst other chapters throw increasingly harder to beat baddies that you'll be happy you conserved some ammo to take them down with. Exploring is a must if you want to keep your ammo levels up as well as experience to level up your abilities/storage capacity.
For the most part though, you WILL need to kill a lot of baddies, but you can dodge past a few and save up ammo. I often opt for stealth kills just incase they might come back later on to bother me. Bosses with the exception of one have required loads of bullets to kill them though.
That actually sounds really good! I want to try this game out, will have to wait for a sale though, I've got enough on my plate at the moment.