An application that appears cluttered or illogical is harder to understand and use.
Aesthetic integrity is not a measure of how beautifully your application is decorated. It's a measure of how well the appearance of your application integrates with its function. For example, a productivity application should keep decorative elements subtle and in the background, while giving prominence to the task by providing standard controls and behaviors.
An immersive application is at the other end of the spectrum, and users expect a beautiful appearance that promises fun and discovery. Although an immersive application tends to be focused on providing diversion, however, its appearance still needs to integrate with the task. Be sure you design the user interface elements of such an application carefully, so that they provide an internally consistent experience.
From Apple's iPhone Human Interface Guidelines.


Amongst the hand-wringing over the choice of colors and animations, and the inevitable kvetching about the need for new video cards, it's worth pointing out the rise of some interesting personalities from within Microsoft. In fact, the most notable thing to learn from Microsoft's recent enormous leaps in the usability and attractiveness of its flagship products is that there actually are personalities at Microsoft.