Maybe I should say: the language is in the range we've heard Pratchett characters do, but the author has never done it at the narrative level. Anyway, the book is its own thing, not a retread.
The interesting Discworld comparison is in my reaction. The old 37-whatever-book turf has a comforting familiarity to me, I freely admit. Pratchett has been wise in adding new characters and locales to his canon, but there are always familiar whiffs as well, and they're an undeniable part of the fun. Reading Dodger, I had to get into the story; I didn't expect that. Silly of me, I know, and it was full-bore momentum once I made the shift.
Dodger's story is all for the love of Dickens, which puts me at a disadvantage -- I ain't read any, nor gotten closer than the Muppets interpretation. I guess Pratchett knows that much of his readership will be in the same boat, because he gives enough context for us to appreciate the pastiche -- or past-iche, pre-stiche, whatever you call a retrospectively-created invisible forerunner to canonical works. Also Charlie Dickens keeps writing down book titles. I laughed.
(Other Victorian characters appear, both real and fictional. I had to look up Angela Burdett-Coutts, and then snuck a peek at Disraeli's wikipedia page too. Sweeney Todd makes an appearance (though not Sondheim's Todd) (though it may be Sondheim's Todd's knife). For a few pages I was sure we were getting a twisted "Scandal in Bohemia" too, but no, not really.)
As for Dodger, he is a fine character. Unusually headlong for a YA protagonist, I'd say. Self-doubt and slow maturation have become conventional in YA stories; we don't often get the adult-protagonist thing of stomping decisively off to get the job done. (Not in a foolhardy way -- that would be "headstrong", quite a different thing -- Dodger is quite self-aware.)