I enjoy using VLC as it has so much user added content that it is constantly evolving.
I find this important because many of the mainstream corporate funded players only get their updates once a month, or a few times a year. This can be very frustrating with the constantly changing encryption and new file formats that are popping up.
Also, for those who are Mac users, VLC also makes a high-quality version for you. So you don't have to worry about reading files.
As for appearance, I find the interface pretty bland, but it does do what you need it to do. I will take functionality over aesthetically pleasing any day.