"The Water Margin" is based on a great ancient tale from Chinese literature. HOwever, it's not the entire story--just a small portion of the text "Shuihu Zhuan". I am certainly no expert on it--and that's a serious problem, as I had a lot of trouble understanding the context for the film as well as the sheer number of characters. Keeping track of them was impossible for me though I assume many Chinese viewers would be far more material with the characters and source material. I wish I could have sat and watched this with a Chinese scholar--and it's very likely you'll feel the same way. The story is about revenge and abuse of power--but I did have significant trouble following the story. And, although it's a Shaw Brothers film, martial arts are not that prominent in the movie. My advice is that if you know the story well, watch it. I have no idea how to score it for you. But, for the average fan of martial arts flicks who is NOT familiar with the story, I say skip it--it's just too confusing and the action isn't enough to keep your interest.
By the way, when this film began, my uncle turned to me and asked a very obvious question--'how are those boats moving so fast?'. This is because the ships' sails are not down and there are no oars--yet the ships are going VERY fast across the water! This is supposed to be the Middle Ages--yet the boats appear to be moving as a result of outboard motors. Could the ancient Chinese have been THAT clever? I think not--though they were darned advanced at the time!
By the way, much of the soundtrack for this film was 'borrowed' from the Hollywood film "Hang 'em High". It's pretty weird, as the original film was a western made to look and sound like a spaghetti western--and now it's in a Chinese martial arts film!