1. You can try maxing out your reputation:
Guide - [Spoilers] Recipe for high reputation in all 4 kingdoms
2. You can hunt down all optional bosses like: King of Korne, Varessa&Mylora&Blafarne, Void Lord
3. You can farm Rings of the Star Traveler to maximise XP gains for you and your companion
4. Finishing all quests
5. Getting all secrets
6. Getting all achievements (EK Supporter III is bugged though)
7. Maximising your setup in any way you decide beneficial
8. Make a new character with different class and difficulty