Perhaps after three brothers, troubled times. The great protector is the most underrated drama ever, especially in recent times. The acting has been superb, along with the music. Shan Mao's theme is the best soundtrack of the series. Despite having martial arts and the early republic era shown in the drama. The presentation has been very realistic and less idealistic. Actually throughout the drama there is a dystopian atmosphere, which is very true of that era in Chinese history. Due to its dystopian atmosphere, despite being a beautiful story. I agree that it reduces its appeal for rewatch value. I my self consider this to be a one time great experience to watch.
However, the series maintains moments of humour from both the protagonists and the antagonists, in a strangely (yet brilliant) manner to balance the drama's generally depressive vibe. Overall, its a very tragic drama and as the series progress towards the end it gets more and more tragic.
In short despite being a tragic drama. It has moments of decent fight scenes, a very unique love story between the lead actors and the best part is the historical accuracy of the events of that time. Along with the change in technology, culture, politics and society shown in the drama of the early Republic of China.