-Gao Chiu plays soccer and becomes a Senator
(this is at the very beginning and establishes the villain)-Chao Gai and six others steal the birthday gifts (really sets the tone with a clever heist story and establishes characters)
-Yang Zhi kills Niu Er over a sword
-Song Jiang murders his lover in a fit of rage
-Lin Chong burns down the fodder depot (Lin Chong's whole story in general)
-Wu Song and the Delightful Forest
-Wu Song kills a tiger with his bare hands
-Elder Brother Wu is Poisoned by his Wife
-Lu Junyi is recruited (this story was made into a movie by Chang Cheh called "The Water Margin)
-Yang Xiong and Shi Xiu at the Butcher Shop
If you find the bits with Lu Zishen a bit boring (they go on a long time,) I'd recommend skipping ahead. He's a very minor character despite how much screen time he gets at the start. Shi Jin is another with almost no plot relevance.
A consistent theme you see throughout the novel is that the heroes are willing to endure any punishment to atone for their mistakes, but the society is so cruel and corrupt that it will not allow them to live. Over and over, virtuous heroes are made prisoners and then inevitably scheduled to be assassinated in some out-of-the-way place. I think that message rings true even today. In a truly corrupt society, a virtuous person is never left alone. Lin Chong gets absolutely gangfucked for no reason over and over until he finally hulks out in frustration.
The stories I've listed are based on what I remember. They're the most important tales in the novel imo. Song Jiang, Chao Gai and Wu Song are primary characters and it's worth it to read their stories. The Yang Xiong story is similar to other stories in the novel about wives who cheat on their husbands, but it and the Elder Brother Wu story underline both the savagery and nobility of the Water Margin. These stories also have some of the most evil characters, who receive a just reward for their behavior.
The adultery stories are probably my favorite.
