I'm evaluating Ext for our project but I think It doesn't suit very well. Please, correct me if I'm wrong:
1)Ext doesn't have data binding or an implementation of observer pattern, so isn't good choice for application whose data change in more complex patterns and require UI to refresh itself to reflex those changes.
2)UI patterns has so many variations that mean something different for each person. But trying to use those patterns names, I would say MVC is not a good pattern for interactive client application that have complex UI logic, something more in the line of MVP is better.
3)Ext UI Components are tightly coupled with not-UI Components. For example, Grid is coupled with Store and Model. We don't need Store and Model, but can't connect our own classes with Grid because there aren't interfaces that define a contract of how Grid interact with data sources.
4)We want our application logic to be independent of Ext. Use our own Model with Ext UI components. With this low coupling, changing the UI components in the future doesn't generate a great impact on our application.
Ext seems to be a whole prescription, not being easy to use each components isolated, permeate deeply in application, to the point of even changing the css style of the whole application.