Imho Ext is a specialty of all the existing UI frameworks, and imho it's shit. Tbh I though it would die directly after being bought by Idera. Even most of the most Senior people left or got fired after that.
Most annoying things (imho): - lock in: all their widgets, and tooling, and everything only works for Sencha products, and is by far worse than the current open source counterparts - price: for a SMB/big-company this doesn't matter, but you pay a premium to use "widgets" which are worse (imho) than open source - Sencha Widgets compile into clunky and non-semantic HTML (thousands of divs), which also impacts performance a lot: simple apps usually have 3-5MB - debugging is difficult as you have to go through their "OOP" layers (can be 5-10 layers) [Java Developers created this Web Framework]
People argue that it's great because many rich widgets are already available and because the framework tells you how do to stuff. But everyone will run into a point in time where something is just extremely hard because of extjs constraints, which usually ends in a hacky solution.