Divinity II, when it works and shows off its best features, does offer a solid experience in the action RPG world. Flames of Vengeance sadly chooses to show off the best features in only a single (albeit incredible) sequence, while downplaying what made the core game work in the first place. Although the combat balance was fixed, other parts were slashed, and the total package feels like the opening half (i.e., the worse half) of the core game.
Still, Divinity II isn't a bad game. If you haven't played it at all, you might want to consider picking up the package deal (called "Divinity II: The Dragon Knight Saga"), which also reworks some of the content from Ego Draconis. However, if you've already played Divinity II, remember that Flames of Vengeance will test your patience; consider that before deciding on your purchase.