Rather than give you a long changelog I thought I'd give you a brief description of what has changed in the 6.0.
1) Firstly and most importantly is a new map, India, China and America have been completely redrawn. Full credit for this goes to Dafool (China/America) and Trin Tragula (India). All in all I think we added something in the region of 100-150 provinces (I'm sure Dafool can clarify). Tonnes of new countries were added to fill these regions too! India also has completely revamped cultures.
2) We added new graphics, more precisely the terrain textures and map overlay from the DaO mod. I still like the Modestus map however I thought it was time for a change, and I really liked the DaO map graphics.
3) Everything (and I mean everything) has been rebalanced. Benefits from missions/decisions, ideas and sliders has been rethought. Claim on X now requires cores!!! and nationalism lasts for longer, and reduces manpower. There are many other changes, some of which are documented in the changelog, but many of which aren't. You should just notice a general difference as you play. Finally, cbs have been reworked slightly. Every nation gets religious liberation which gives 25% bb. Holy war is reserved for muslims, catholics and orthodox - it gives 50% bb.
4) Religions in the east redone. Hinduism is in its own group. Buddhism is split into Theravda and Mahayana. They are in the same group as Shinbatsu Shugo and Shenism.
5) I added loads of new events and decisions to add a bit more flavour to certain countries and generally make the game more interesting.
6)There's generally just loads of other stuff which I can't begin to start describing. If you noticed any new features you liked please flag them up for other people to know about.