They just changed the zombies to have line of sight targeting, before they would chase you forever and inevitably get you if you dont kill them. Now if you can break LOS they will stop chasing full out then try to investigate where they last saw you.
The zombies are hardcore, they run like dawn of the dead and you need a 7.62 or equivalent weapon to one shot them, unless you head shot them, which is one hit with any gun. I only raid for loot with my suppressed M4. Unsuppressed weapons aggro zombies from all around when you fire which makes your world go to shit real quick. Once you aggro some and you are forced to defend yourself, you must aim for head shots or you will just make a lot of noise before you have to reload and they knock you down and eat you.
Melee weapons just got added a day or two ago and are just proof of concept atm, I have a hatchet but I haven't used it on zombies yet, only to cut firewood, but I have heard they will one shot to the dome as well.