That's not really working well at the moment. In A20, I had several zombies stuck in shelves or other objects that they tried to crawl under, for example.
I see the problem a lot in the warehouse areas of POIs such as the Working Stiff or Savage Country stores.
Well I didn't mean to imply it was all done. I meant to state for the record that the REASON zombies were given the ability to crouch was to improve their pathing and help them not get stuck in places they typically would get stuck. That the process isn't finished yet doesn't mean that TFP did to thwart certain strategies that they deemed "wrong". And nobody, least of all me, is trying to claim that the work is considered finished.
One area where it is working much better is in attics where the sloped ceiling comes down to meet the floor. In A19, the zombies couldn't path in those areas and (at least in my games) they scuttle around in attics under those low sloped ceilings beautifully now. They also had problems with some of the irregular holes in walls and some of the broken windows which they now crab walk through (in my experience) without much problem.
But they do get stuck still in some circumstances and sometimes choose to duck when they shouldn't because even ducked they wouldn't be able to get under the obstacle they are trying to.
Whatever improving the pathing means for the Fun Pimps. For example, I'm not a fan of the Area Destruction mode. It kicks in way too often at the moment and causes problems with certain playstyles like using electric traps or in melee bases.
Area destruction is actively undergoing tuning according to faatal. There was a bug that prevented most zombies from going into destruction mode and now that bug is fixed and it is truly working for the first time. Faatal admitted that they will probably have to adjust the values on it and agrees it is happening way too often at the moment.
"Improvement" in pathing as defined by the developers is making the pathing more versatile and able to help them traverse the complex landscape and interact with more of the world. So having a destruction mode option that turns them from their normal path to something else is an improvement over not having the option. Having an option where the zombies can interact with blocks above them and below them instead of simply whatever is straight in front of them on their horizontal plane is an improvement because it increases their interactivity with the world. Having both long paths and short paths available to zombies is an improvement over having only long paths because it adds a variety of behaviors and abilities randomly among zombies and their sense of exactly how to get to the player.
"Improvement" in pathing is not defined by whether a given player likes the current pathing or not. You may not see the changes as improvements for your playstyle but that is subjective to your own experience. Objectively, all of these changes have been improvements and now the programmers simply need to adjust, debug, and tune things to get the behavior results THEY want which may or may not align with what we want.