Alas for JK Rowling. Like Voldemort she failed to foresee that it could only end badly. The thing about writing an episodic story is that, unless you are Tolkien or Douglas Adams, you are going to run out of steam at some point.
The author commits many crimes against writing in this final book: The plot is patchy and slow including such sins as an endless, pointless and boring camping trip (sadly, the reader cannot leave like Ron) and Voldemort’s wild goose chase after the Elder Wand
Plot devices such as the unexplained reopening of the connection between Harry and Voldemort are lame and require the reader not only to suspend disbelief willingly but to forget that such a thing even exists
The many exit clauses used to resolve difficult situations are simply ludicrous - like, the gormless Crabbe who at 17 cant pronounce words longer than 2 syllables but can produce the Fiendfyre curse, so powerful that it destroys Horcruxes, so obscure that Hermione the all-knowing is ostensibly ignorant of it. Or how about - Ron being able to speak Parseltongue having heard Harry do it once? If it were that simple surely smarter wizards would be able to do it too. Snape for instance, who must have heard Voldemort speak it many more times than once.
Weak, one dimensional characters haunt the book. Harry, Ron and Hermione are larger versions of their 11 year old selves. There is no perceptible growth or change in their essential characters from the first book to the last. The only characters who have unfathomed depths are the ones who are dead or are about to die - Dumbledore, Grindelwald, Lupin and most importantly, Snape.
Snape. Despite JK Rowling’s best efforts her greatest creation is neither Harry nor Dumbledore. Snape has taken on a life of his own that Rowling seems unable to control. He is the monster to Rowling’s Frankenstein. More than Harry, he fits the definition of protagonist having faced moral dilemmas, struggled for identity, and earned redemption by rising above his essential nature. Rowling clutches at the coattails of her most complex character by revealing him to be impelled by love. In doing so, she exposes her own failure, along with Voldemort’s and Dumbledore’s, to understand Snape.
His love for Lily is buried with her - he has no love for her son, that much is clear. Snape’s motive is revenge - revenge, by betrayal, on Voldemort who killed Lily and revenge, by killing, on Dumbledore who failed to protect Lily. The revelation of Snape as contained in the final book is not that he was an essentially good man and hero but that he was the opposite and chose to do something noble simply because that was the means to his darker end. His love for Lily was not his saving grace, it was his fatal flaw and he paid for it with his life, as all tragic heroes must do.
Having racked up an impressive body count and provided 15 seconds of fame for most characters no matter how improbable (Molly Weasley, unable to battle boggarts, finishes off Bellatrix and that’s just one character) Rowling attempts to tie up the loose ends with a badly written, finger-down-throat epilogue that closes this truly horrible book. No self-respecting publisher would have touched Deathly Hallows if the first 6 hadnt been written. And so ends Harry’s magical journey of 7 years. Not with a bang, but a whimper