Avada Kedavra, although all the curses have had so much emphasis put upon them, is just some ordinary spell that just needs some extra concentration because they're a little more risky and can cause greater harm to humanity that any other spell really.. they're only so important because they are so lethal and can be used in a stealthy manner that the ministry had to put into a spotlight to keep it from happening (which doesnt work) and to put more fear into people about it.