I started on 3(.5?) and helped with a migration to 4 (which was a disgusting mistake of a process on our end). I like the format of their docs -- JSDuck was my favorite docset for a quite a while. I also enjoyed their methodology for constructing views and view hierarchies. Ultimately, I'd say I was a fan of what they were doing, I just think the implementation was rather shoddy, and the docs were frequently wrong or outdated, and (as mentioned) support was not good. When I got to React, it actually did bring back some memories of Ext, but without the full MVC hierarchy around views.