Although I am not so well acquainted with the text of "Notre Dame de Paris" as I am with "Les Miserables", it seems to me that there are a number of noteworthy similarities between these two works in terms of character and themes.
Both have as their central character someone who has been wronged by society yet who rises above injustice and prejudice, displaying understanding, tolerance, and love, not so much in spite of their treatment, but more as a result of it. Each learns the importance of love and the necessity of thinking of others to give value to one's life.
Quasimodo, like Valjean, has the strength of character and independence of thought to go against the accepted order and stand up for what he believes to be right. Quasimodo is willing to risk eternal damnation by flaunting Frollo's instructions, doing so not only because he loves Esmeralda but because this love leads him to doubt Frollo, his authority, and the accepted nature of justice.
Frollo, like Javert, is unbending and highly principled, seeking to defend and protect society by means of the law which is enshrined by the Church. Also like Javert, Frollo faces a crisis of faith - his principles are profoundly challenged by his carnal feelings for Esmeralda, as a result of which he abuses his powers and frames Esmeralda for a crime he himself committed.
Javert's crisis comes toward the end of "Les Miserables", while Frollo's forms, to a large extent, the basis for the narrative in "Notre Dame de Paris". One can feel greater sympathy for Javert who has remained true to his principles - it is his dogmatic and blinkered manner of exercising his principles which leads to Javert's problems. Frollo actively abuses his power to protect himself, but also the very position of the Church and the law in society.
Phoebus and Fleur-de-Lys may, perhaps, be compared at least to some extent, to the Thenardiers. Both couples are quite untrustworthy, selfish, and unprincipled. Phoebus's head is relatively easily turned from Fleur-de-Lys towards Esmeralda, though eventually he returns to his first love, allowing Esmeralda to be blamed for a crime and laying responsibility for his behaviour at her feet. He takes the easy route of self-preservation while at the same time causing Esmeralda to pay the ultimate price for his indiscretions.
Fleur-de-Lys may be viewed as a sort of Lady Macbeth figure, pushing her fiance along this course of action while avenging herself on the woman her fiance preferred.
Gringoire is a sort of Marius-like figure, idealistic and relatively innocent, providing contrast to and illumination of Frollo and Phoebus.
Clopin may be compared to Enjolras, leading a revolt of the people against the accepted authority and its perceived injustice, while standing up for the common people.
Finally we come to Esmeralda herself who, like Cosette, serves as the catalyst for all these events and emotions. Also like Cosette, her character is perhaps less important than the emotions she provokes in others and the events for which they, in turn, are responsible. Neither Esmeralda nor Cosette actually contribute a great deal to the advancement of the narrative, but serve instead as the inspiration for others.
It seems to me that Hugo is dealing with similar themes in both novels. Love (spiritual and physical), inner beauty and goodness, tolerance, justice, faith, morality, and the very structure of society - all are dealt with in both novels, and in surprisingly similar ways.
"Notre Dame" was of course the earlier work, and by the time Hugo came to complete "Les Miserables" (over a period of some twenty years), he had perhaps mellowed a little in his criticism of religious intolerance, showing both positive and negative potential influences of orthodox religion, but preferring a sort of non-ecclesiastic spirituality. Hugo does not appear to reject the notion of God's existence, but rather criticises the blinkered and dogmatic approach of the Church and its influence and authority over public morality. He points out the unnatural and untenable position of a priest charged with responsibility for public decency as he discovers within himself human weakness and sexuality which lead him to break the very laws he represents.
In "Les Miserables" Hugo again stresses the unnatural condition of nuns leading their lives in isolation in a convent, though he also shows a more human and useful side of religious devotion in the shape of the Bishop of Digne. It is worth noting, however, that the Bishop is praised largely for the practical good he has done, rather than simply for his devotion.
I think Hugo also created a more successful central character in Valjean than he did in Quasimodo. The reader has, of course, great sympathy for Quasimodo, and one is forced to confront one's own prejudices concerning appearance and the qualities one holds in high esteem etc.. However, there remains a doubt as to the total effectiveness of Quasimodo as a hero. The reader undoubtedly sympathises with his plight and, through him, finds fault with various aspects of society, but it is very difficult to truly identify with such a character. He certainly pulls at our heartstrings, but we are almost in a position of superiority, comfortable in our disapproval of the injustices he has suffered, and safe in the knowledge that we are unlikely to suffer in the same way.
Valjean, however, is quite different. The injustices he has suffered could be encountered by any man desperate enough to commit even a minor crime or indiscretion. Every man is capable of surrendering to his circumstances, becoming self-centred and losing sight of the needs of others. Valjean is a more universal hero who is surrounded by equally recognisable characters with whom we may more readily identify.
There would appear to have been something of a progression in the telling of the tale, though fundamentally I think Hugo is dealing with similar problems and observations of life in each novel.
As I indicated at the top of this page, I know "Notre Dame" considerably less well than "Les Miserables", and so the ideas contained in this page may well be proven incorrect!
I would be delighted to hear from anyone wishing to discuss these or any other ideas further. I can be contacted at:firstname.lastname@example.org