Now that the infected are able to sense me so much easier, I believe the fact that survivors can't crawl up a stair or over a threshold has become a problem. Crawling my way through these zombies just to have them see me when I have to crouch to go over a tiny threshold is annoying. Also the zombie respawn, to me, seems very over the top, I ran into a medium yield barn, killed 17 zombies around 1 barn in the middle of nowhere. Looted said zombies and the various piles, 60-90 seconds tops, as I leave the building, another dozen zombies appear behind me and aggro. I manage to live and kill all the zombies but using 30 rounds (minimum) on 1 building in the middle of nowhere is going to really curtail any survival time. I enjoy the aggro changes, leading to more stealth and more killing, but that quick respawn is just too much.