Yeah....see.....I like my simulated combat to be vaguely realistic. Zombies get silly fast.
The zombies are just part of the scenery for the most part. They can run after you but once line of sight is broken they stop. If they corner you in force you might get hurt trying to get away, but it's usually pretty minor. They are supposed to behave kinda randomly, so seeing one run to a building isn't always a sign that another player is around. There is also player controlled zombies that adds a little more to it, but they're still easily killed unless something goes terribly wrong.
Of the Arma3 mods I've played, I think the firefights in BP are the most satisfying. You might run around for miles and not see anyone, and then suddenly stumble into the wrong area and get overwhelmed quickly. There's a class system whereby you are awarded points for killing other classes not friendly to yours (and helping those classes friendly to yours with food, water, medical, etc), so while it squarely a PvP mod, it's not pure KOS all the time. Target ID is important if you're actually trying to play your character the way it's meant to be played, which the majority do. It's also got an expanded weapon lineup, so you've got lots more to play around with than the vanilla Arma3 MX rifles and such.
Shoot me a PM if you wanna monkey around with it. I play with a group of guys who usually aren't dummies and can help get ya up to speed.