Part of truly appreciating someone is accepting them the way they really are.
When you do this (instead of being fixed on your own mental image of how you would like that person to be) is when you truly start to see their grandeur, to hear their wisdom, to admire their qualities.
Just as things rarely come out exactly the way you plan them, people are almost never the way you define them in your head- sooner or later you will be surprised to see something different, and often better.
When you are constantly comparing your mental list with reality, you will most likely be disappointed. Not because the person is flawed (although no one is perfect, chances are they're tons better than your limited image of them) but because they will not rigidly fit into your closed off made up profile.
Just as intellectuals who have too many books in their head often think they know more about life than God herself, how do you expect to know more about the other person than that very person?
Allow them to show you. Relax. Sit back and enjoy what you see, hear and receive. You will begin to see so much that you were missing. You will begin to love not who you think they should be, but who they really are.