Divinity: Original Sin - Enhanced Edition
54 Achievements
120-150h
GOG
Grande finale
You have totally, completely, and utterly finished the game.
12.8%
How to unlock the Grande finale achievement in Divinity: Original Sin - Enhanced Edition - Definitive Guide
So the wording on this achievement is a little deceiving. This simply requires you to beat the game. When I finished the game I had two quests that couldn't be finished due to the series of choices I made.