Well, 'A Murder of Crows' is a must - read. It shows the complex relationship between Swamp Thing and the creatures in the swamp. Also, 'Down Among the Dead Men' is really good. It dives deep into the horror aspects of the Swamp Thing world, with great art and a chilling story.
Definitely check out 'The Saga of the Swamp Thing'. It has a lot of important elements that introduce new readers to the whole concept of Swamp Thing. And 'Tales of the Green Lantern Corps' which has some crossover stories with Swamp Thing that are both fun and informative for those new to the character.
The main characters could vary depending on the specific version or interpretation of Swamp Stories. But typically, they might include brave adventurers, mysterious swamp dwellers, or perhaps magical creatures.
Grave Robber's Chronicles: Snake Swamp Ghost City was a very popular novel. The ending of the fourth edition had already been released. However, it should be noted that due to the popularity of this work, there may be different versions of the continuation or adaptation.