How do you value a feature? My own estimation is based on the amount of effort that it took, but the client has a totally different metric. The value of a feature for a client is directional proportional to the amount of pain it removes, with complete and utter disregard to the effort it took to implement.
That is completely reasonable approach from the client point of view, naturally. But I wish I could always get a "Wow, that completely rocks!" for those features, and something better, "Oh, you finally got it to work" for the stuff that had me pulling hair.
As an aside, this leads to managing the customer expectations, the classic example of which is of the mockup screen that looks real, but I have a whole lot to say about that, at a different post.