The only thing I didn't like about the Elder Wand subplot was that it was dumped on us in the middle of the final book. Every other plot point, be it related to a lone book or multiple ones - such as polyjuice potion, portkeys, the pensieve, etc - was foreshadowed or introduced in some way, shape or form. There was no mention of the Deathly Hallows, the Three Brothers or the three objects in any book. Sure, Harry had the Cloak, but it was never expanded on or implied to be more than simply an Invisibility Cloak, and yes, the Resurrection Stone was in The Half-Blood Prince, but as far as we knew it was just a horcrux. There was so much potential for foreshadowing of the single most important plot point to the series and it was wasted. Be it the symbol appearing on a book in the library (like when Harry went to the Restricted Section in his first year), or the ghost professor mentioning the CHamber of Secrets as being as much of a myth as the Three Brothers or whatever, there was plenty of opportunity. Even the whole sub-plot of Harry witnessing Voldemort searching for the Elder Wand could have begun in the previous book.
Also, the epilogue felt as like bad fan fiction. I can see what JK Rowling was trying to do; by writing it she made it such that there's no need for a sequel, but that didn't stop the fact that it was enough to potentially ruin the book, if not the whole series.
