View Model Lifecycle as starters, the amount of HTML, CSS and JavaScript boilerplate code that got generated leading to lenghty debugging sessions, and the way most JSF frameworks were basically incompatible with each other.

Example, using RichFaces, and then trying to use something from PrimeFaces, IceFaces, or something else Faces, was always open to surprises mixing their lifecycle expectations.

I was involved with a RichFaces based JSF framework, during three years, and afterwards going back to something like plain JSP and tag libraries felt quite refreshing.