So I was re-reading the series today, and something caught my eye. In the early books people are constantly talking mad smack at Neville for being a shitty wizard, but then you get to book five; and then you see that he has been using his DADS WAND. It gets ruined in that book, and from that point on he gets his own wand, and he is no longer considered a poor wizard, actually quite skilled.
Now why does this matter? Because in the books, it is firmly established that the "Wand chooses the Wizard". This is carried over in the movies, when Draco Malfoy attempts to use his mothers wand in order to corner Harry in the room of requirement, and comments on how it does not work right for him.
It is also in the last book, when Harry has to use the blackthorn wand that Ron obtained from a snatcher.
Basically, if you are using a wand that does not choose you, it will feel wrong, and perform extremely subpar. Neville, up til the sixth book, was using a wand that did not choose him; he just inherited it from his father.