Here is a portion of my personal "take" on love:
As human beings we exist to love: people, creation, expression, ourselves... all forms of love are a celebration of life itself and the reason we are. Love gives life purpose, whether it be love of others or of a task or of a faith. I don't think we would have been imbued with souls for a baser or less grand reason; God would be lonely all by Himself in the universe, I think. What's the point in creating and existing if you have nothing with which to share love?
I'm sure you meant romantic love, however, so I shall not digress any more.
Love is an integral part of the human experience; I don't believe you can find true happiness without having felt love. Even if you lose it, it was worth having because it enriched and expanded the realm of your heart and soul. There is nothing more beautiful and moving than seeing love in the eyes of the one you care for, who understands and appreciates you for who you are, flaws and all.
Some of the attributes I find necessary in a lasting relationship are trust, forgiveness, understanding, patience, and humor. You have to have a strong emotional base upon which to build romance. As Khablan said, you have to be friends first and foremost because passion and romance probably won't last forever.
Another thought: the one you love can and will cause you pain. If you've been with someone for a long time and have yet to be upset or argue I would venture to guess something is being hidden or suppressed. We want relationships to be perfect and expect that when we find "true" love nothing bad will happen between us (especially when we're young and inexperienced) but this is a fantasy. No relationship, romantic or not, is ever free of mishap. Of course, this does not mean it isn't still wonderful. If you truly care for someone you simply have to be able to forgive and move on.