This is a book that I'd recommend to undergraduates studying Dickens or general interested readers: while Mullan's academic credentials are impeccable, this isn't a scholarly book in that it doesn't propose or argue a thesis, and doesn't make any interventions in the field of Dickensian scholarship.

What is does is claim that Dickens was an inventive, ingenious writer (sure, he was, but I don't think anyone's arguing about that, are they?) and then give numerous examples of his themes (hauntings, say), techniques (describing smells, employing clichés for deliberate affect, changing tenses) and characteristics of his writing (coincidences, naming). In that sense, there's nothing new here and Mullan doesn't analyse the significance of what he's describing, simply gives us instances across the Dickens canon.

I'd say that if you're not familiar with the texts then this will likely give away spoilers. It's an interesting read, though, and certainly Mullan's own enthusiasm comes over so that you'll yearn to revisit Dickens' novels.