There's still every reason to be wild about Harry.
Many authors avoid fictional growing pains by either freezing their characters in time, à la Peter Pan or Alice, or shuffling them off stage when they get beyond that wide-eyed precocious stage, as C.S. Lewis did with the four young Pevensies.
(In fact, Lewis went so far as to punish Susan for growing up by denying her access to Narnia in "The Last Battle.")
Frankly, creating believable teenagers in fiction is a tougher job than is usually acknowledged. Which is why it's nice to see that Harry's turning out so well in the sixth book of the series, Harry Potter and the Half-Blood Prince.
His (admittedly justifiable) sullen anger from "Order of the Phoenix" is gone, and in its place is a determination to enjoy life. As a result, the first half of the book offers a sense of lightness to balance the ominous doings to come. Savor the trip to the Weasley twins' new prankster emporium, as well as the banter and the teenage crushes, because, as Rowling has indicated, the casualty list continues to rise, and Book 6 does not come equipped with a happy ending.