What is the nature of love in Harry Potter books 1-5?
What is the nature of love in Harry Potter and the Philosopher's Stone through to Harry Potter and the Order of Pheonix? Is there much love in the book?
This is really quite broad given that we can see many different types of love going on in these five books.
I would say that the most important characteristic of true love in these books is that it causes a person to be willing to sacrifice for others. You can see this most clearly in Harry's parents. We know that they sacrificed themselves so that Harry could live. Lily's love and sacrifice, in particular, allows Harry to survive his confrontation with Voldemort/Quirrel in Book 1. Harry himself shows a tendency to be willing to sacrifice himself for others at many points; so does Ron when he lets the chess piece hit him (not knowing if he'd survive) in Book 1.
There are many other kinds of love in these books but this aspect of love is the one that Rowling seems to concentrate on the most.