- removal of global $action
- removal of Xml::hidden()
- broken Output::add() (had to migrate to resource loader)
- various parser tag bugs
- removal of MessageCache::addMessage()
- removal of ts_makeSortable() (javascript)
- brokage of WikiEditor adaptation
- MediaWiki:common.js no more loading by default (security)
- addHandler() javascript broken in IE8
Most of these were deprecations, am I correct?