My company uses IWS almost exclusively. We had been largely an RSView/FTView shop, but had a manager come in with IWS experience and he got the rest of us experienced enough to use and like it.
We use it for small (300-tag) to medium (8000 tag) systems. We've had some glitches, but no more than most products. I cringe when I have to go back to PanelView Plus for anything.
While I would prefer to use Ignition, the Java dependence and incompatibility with C-Python libraries makes it unsuitable for us. We have a huge amount of Python skill in the company, but it relies on libraries for which Jython equivalents just don't exist.
IWS's use of VBScript is a decade out of fashion, but it's simple and powerful enough that most of our guys can make it do what they want.
The acquisition by Schneider was alarming to me; the local Wonderware office periodically pokes their nose into our projects, trying to convince the end customer to buy licenses from them at 2x the cost. So far we've been able to stick with our OEM sales rep at Indusoft.