The Pickwick Papers was Dickens's first novel. It was begun as a series of illustrated pamphlets, and it was only as Dickens's writing caught the public fancy that it began to take on the characteristics of a novel. So it's a story that changes form as it goes along, but is always entertaining and often moving.
The plot is essentially an account of the adventures of Mr. Pickwick and his friends as they travel about England in search of novel experiences. Because of the nature of its publication, each of the early chapters is more of a standalone story full of slapstick comedy and just a touch of satire. As the novel progresses, it becomes more of a complete work resembling Dickens's other novels. There are moving scenes of debtor's prison, scathing commentaries upon the law courts, etc, just as one will find in his later novels. Reading The Pickwick Papers gives you the unique experience of witnessing from chapter to chapter the literary emergence of one of the greatest novelists of all time.
My full review is here.