Disinterred from email comments I made back in 2008...
I did eventually finish "Deathly Hallows" -- and it wouldn't be quite fair to say that it was that which put me off the whole Harry Potter scene, but I haven't felt any urge to reread the other books since :-DI'm afraid that "Deathly Hallows" does tend to play to Rowling's weaknesses. Her Voldemort comes across as neither particularly frightening nor especially intelligent -- not much of a threat (compare to the version evoked in The Prefect's Portrait, for example, which is equally consistent with canon but comes across as considerably more capable and dangerous). She can't depict either romance or grief convincingly, and the use of CAPITAL LETTERS does not convince this reader at least of the intensity of the characters' feelings ;-p
The sudden introduction of the Deathly Hallows is both almost pointless (they really aren't necessary for the outcome of the plot) and feels like 'cheating', since they give the impression of having been made up on the spot to be sprung on the reader after seven books -- it is not a revelation which suddenly makes sense of everything else in retrospect, as it should be, but an unnecessary extra which appears to have been bolted on to satisfy the requirement for a fresh magical gimmick in every book. They also offend my sense of the shape of the story since they really serve only as a detour -- basically, as a time-waster for Harry & Co.
The attempt at developing the Malfoys is too little, too late ("Spinner's End" was much more promising in that respect) although even the attempt is welcome. A lot of good characters are wasted: Slughorn, Snape of course, Lupin, Tonks, Ginny. Dobby's death is wildly overwritten -- I don't feel it at all, and consequently don't find Harry's supposed reaction credible. *Telling* us /ad nauseam/ what he is allegedly feeling is not an adequate substitute for evoking the actual feelings! (In fact, this goes for all the other 'deaths' -- it's like being battered around the head with a large club labelled "Oi, Look Here, Harry is Feeling Emotion".)
The whole 'Dumbledore is homosexual' business (which is *not* part of the book) strikes me as a shocking piece of misjudgement to put it charitably (the uncharitable conclusion would be that it was a publicity stunt/piece of special inclusivity pleading) -- for Dumbledore to be fascinated and led astray by the other boy's *ideas* is a far more powerful and thought-provoking concept than the implication that he was merely interested because he fancied fondling his handsome contemporary :-(
And of course, the long-promised final paragraph, supposedly written long since (the one ending with the word "scar"), is not in evidence. Instead, we have a decidedly limp epilogue which reads like a lame piece of 'when they were all grown up' fan-fiction...
The most plausible explanation of the problems with "Deathly Hallows" that I've seen put forward is that the book was indeed planned at the same time as "Philosopher's Stone" and as a result has little more depth or maturity -- but that the subsequent books in between had developed characters and sub-plots to a degree that simply could not be squeezed neatly back into the strait-jacket of the original concept. In other words, by the time she came to the planned ending it didn't really fit the story any more and had to be shoe-horned on. I find this plausible because I've had that experience myself!
Frankly I don't find the climax at all satisfactory: she is not terribly good at writing action scenes, the whole Harry's-blood-in-Voldemort thing is terribly convoluted, the enemy are not written as particularly threatening (compare "Water-horse" for example :-p), and the bits that are supposed to be highly emotional just fall painfully flat. I find the climax of "The Prefect's Portrait" a considerable improvement -- even though of course Harry couldn't possibly have defeated Voldemort in only his sixth year ;-) (And in that decidedly female-oriented version, he doesn't have an awful lot to do with the defeat, really...)
Rowling's talent was always in creating fascinating background details of how her created world actually worked. Emotion and ambiguity were never her strong point. That said, it's rather dispiriting to compare how much better she was at evoking the affections, excitements and resentments of the 11-year-old Harry -- perhaps the trouble is that she really is a children's writer and not an especially good teenage writer :-(
(Yes, I liked "The Prince's Tale" -- but it's ironic that I found myself thinking 'Good, she's got Snape right' as one does with a piece of fan-fiction! She completely wastes the character in the end, though: it's both unsatisfactory that his death is more or less coincidental given the amount of development that has been put into the character over the previous 5-6 books -- you expect him to achieve something significant -- and decidedly unconvincing as a piece of planning by Snape/Dumbledore. It is basically only by coincidence that Harry ever finds out the truth, since he happens to be around at that precise moment -- not much to hinge the supposed big reveal of your plot upon.)