Unfortunately you don't really get to witness the shadow curse lifting, at least not in any way that provides content, gameplay, or exploration.
The most you get is a cutscene when transitioning from the end of Act 2, to the beginning of Act 3.
On an unrelated note. You can't return to Act 1 or Act 2 locations once you begin Act 3. Make sure you head to the mountains and do the content there before you leave.