Contrary to the lighter first season, the second season treads a much darker path as it focuses on the fight for the throne among the princes now that the Crown Prince's seat is for anyone's taking.
Crown Prince Yin Reng has lost power, and yet Nian Shu Yuan chooses to stay by his side. As Empress Dowager Xiao Zhuang has fallen critically ill, the two leave the palace to offer their prayersthat she may get well. Kang Xi sees this and becomes moved by their sincerity. The 1st Prince's plot to conspire against Yin Reng finally comes to light which leads to Yin Reng being reinstated as Crown Prince. At the same time, Nian Geng Yao gains military strength and political clout after returning as a war hero. The 4th Prince who has always hidden his strength begins to make his move in his ambition to take the throne.
You also get to see a lot more interaction of prince 4. I ended up skipping parts because some of them got very repetitive.
Overall, i would watch it if you have time, but if not, its a skip.