I'm not a UI engineer so I'm not necessarily qualified to answer from a design perspective. As a user however, what attracts me is logical and efficient design. For example, like many UNIX-heads, I prefer a command prompt for the vast majority of my work, for the simple reason that I can't get so much done more easily or quickly than through a GUI. Depending on the task, a GUI may be better (e.g. photo galleries, or photo editing beyond simple conversions, page layout, etc.).
When it comes to the average user however, interfaces are designed to try and simplify a concept that's not always logical to the uninitiated. A file browser distills the concept of files and folders into graphical representations people can map to real life objects they understand, even if they have no idea what a computer file really means in terms of sequences of bits. The use of a mouse cursor is meant to map a visual aid to the task of manipulating these virtual desktop items as though it were an extension of the user's hands. Therefore any interface that does this in a more natural or more appealing way (and beauty is in the eye of the beholder here) is going to be preferred for that user.
To me and many others, a minimal GUI with a heavily text-driven interface is appealing because I find mouse movements very inefficient. Text is natural as we're all used to reading and writing in various forms. Yet to many other people, a command prompt is intimidating because it seems cryptic and unpolished. Different criteria simply work better for different audiences, and what's most important at the end of the day is how natural a UI is for someone to use given their background. It's not necessarily just what color the buttons are or what order a menu is in or what kind of shading effect you use. Those things can certainly be factors but ultimately I think it's how instinctually easy it is for a user to find necessary functions and understand their effects.