Roleplaying is often seen, by those who don't indulge, as a weird waste of huge amounts of time and effort. And it is true, it not only takes hours to play small amounts, but it can involve an amazing amount of research and preparation to make a game work.
But when it does work, when the "plan comes together", I can't think of anything more satisfying. All the effort that was put into the game or the character suddenly all meshes together to form a creative thing that has a life of its own.
Different things bring this situation to life, depending on whether you are in a Con game, or in a campaign game. Con games need to be a lot tighter than a campaign game - the characters need to have some form of handle for the players to pick them up by. Con games fire when the players really find that they can grab the character and go and the plot is a good one. This seems to be trite, but too often the plot and the characters/players don't mesh and the session is 'ok'. No one plays for 'ok'. People play for the three months of anecdotes and memes that never go away.