My philosophy is that once you get people compelled enough to sit down and play the game, the whole way you make the game successful is by giving them enough unique ways to do things. First, let them deal with pulling levers and things like that for a while. Then after they've mastered that, you give them something else to do, like getting through doorways by blasting them down with a cannon Next, you give them a monster-finding quest, followed by logic problems to figure out. You pace it that way. Assorted activities and the diversity of activities are what makes a game rich in my mind.
Richard Garriott