Someone asked this question on HP and I was loving the response and thought I'd share:
"
Should I read the Harry Potter series considering the fact that I have already seen the movies numerous times?"
The response:
"Do you know what color Harry's eyes really are and why they are important?
Do you know all the Weasley kids?
Do you know who Peeves is?
Do you really know and understand why Snape mistreated Neville so much? Did you even notice that Snape mistreated Neville more than others?
Do you know what an animagus is?
Do you know and understand Voldemort's history?
Do you know what happens to Peter Pettigrew in the end and why?
Do you know who are all the Marauder's?
Do you know who was the Half-Blood Prince and why he was called so?
Do you know who Squibs are?
Do you know why Rita Skeeter's character is important and where it was important?
Do you know and understand Snape's history?
Do you understand Dumbledore's character, his behavior towards Harry right from the 1st book, and what was his overall importance to the series?
Do you know the history behind Lupin and Tonks? How they ended up getting married? Do you know who Teddy is?
Do you know who Phineus Nigellus is and why he was important?
Do you know who Barty Crouch Jr. is and what his backstory is? Do you know who Winky is?
Do you know what happens to Harry's wand in the end?
The above represents how much you will lose out on by not reading the books.
So it's quite simple. Read them."
Source
Do you agree? Books > Movies overall? Or are some movies enough in some cases?