I like that it's completely customizable to fit your needs/requirements! It can be used for anything from simple websites with basic functionality (like landing pages) all the way up to complex web apps or portals you'd use in an enterprise setting.
Sometimes there are bugs but they're usually fixed within hours of being reported so we don't have much issue here at this time. There is nothing about WSO2 which really bothers me as far as dislikes go - everything works well together when using their products. We've been able to create highly secure environments without having to spend hundreds if not thousands of dollars per month by utilizing these services provided through them.