I finished reading the final Harry Potter novel last week (possibly the last person with any interest in the series to read it). As I've got a Flexi Day off work today, I thought I'd share my opinions. In case anyone reading this still plans to read the book, I'll try to avoid giving any "spoilers".
I thought the book was good value, and an appropriate end to the series. I've now read them all, of course, and enjoyed every one with the possible exception of number 5 (The Order of the Phoenix). Books 1 to 4 were all great fun although - as many viewers have pointed out - the darker side got more prominent as Harry grew a little older. Phoenix may have coincided with the peak of J K's wealth, or a feeling of security, complacency or whatever - or it may have just been that her publishers got so overawed by her success that they didn't dare prune 30% off the book's length. The consensus (with which I agree) seems to be that drastic editing was what was needed. Anyway, she seemed to be back on form with number 6 (The half-blood prince), which had some interesting twists and turns and was quite effective in "killing off" a major character.
Unlike some others, I didn't find that Deathly hallows "sagged in the middle". I found the interaction between the characters genuinely moving at times, and having an occasional minor character die at various points brought it home that, as this was the final book, all the characters were dispensable. Towards the end, there are some surprises around the motivation of a couple of characters, which at times struck me as unnecessarily convoluted and made me suspect that Ms Rowling has read too many Agatha Christies!
If the climax didn't work 100% for me, this is probably because the author was hampered by having to make things very literal at times, to avoid readers (particularly children) complaining that they didn't understand what happened. So, while saying "So and so was dead" falls a little flat in terms of prose, it was probably necessary. Again, without giving away the plot, let's just say that the series is brought to a fairly definite conclusion.
Overall, I would have to recommend the Harry Potter series to anyone who loves books - not just children and young people. While the books don't have the philosophical depths of (say) Philip Pullman, they're just as readable and almost as entertaining.