A clip from a recent episode of Community¹ says it best:

Found via a great article by Daniel Sinker, titled I'm Starting to Think Lego is Evil, that includes an advertisement that I can't imagine seeing today for Lego.

My son and I love playing with Lego together and while he likes the idea of some of the predefined sets out there ², in the end he typically ends up just playing with it and building random houses and planes and other things that are just fun to try to make from the little pieces.

1. If you're not watching and loving Community, you're not wired right. ↩
2. I have an unwritten (until now) rule on Lego and movie tie ins. The movie has to have been released at least 10 years ago before you're allowed to buy a set based on said movie. So in other words - Star Wars is the only Lego/movie set allowed in our house. ↩