“Simplification is a non-negotiable must, but really good user interface design has to offer other qualities too. One is fun...” from The digital challenge: Making easy-to-use devices.
Sure, a lot of designers and product managers require their products to be simple and fun to use. The problem is making buttons puffy or glassy does not, by itself, make interaction fun (nor simple, for that matter). Fun is really, above all else, about the gestalt experience and better defined as something that feels effortless, an activity a user actually enjoys doing.