Turrets, tank drones, chicken walkers. Basically the worst stuff isn’t anything otherworldly, it’s the remnants of human civilisation and weaponry. Perhaps it was the same way when you played.
Mostly, be damn careful when exploring new territory (drive slowly!) and when on foot, keep a pinch of meth on you in case you need to make a swift getaway. Turrets and chicken walkers and the like can be taken out with a long-range rifle, but tank drones I dunno about.
Oh yeah, and be careful when around zombie technicians now. They have electromagnetic bionics that can actually yoink metal weapons right out of your hands at range. Just a heads-up.