- The buttons aren't styled like Cocoa buttons
- The gradient is non-standard
- Why is there so much lime green?
- Why is there a lime green border?
- The images don't look like they scale well, they look blurry and not very well defined, even in the screenshots
It's supposed to be a Mac app but it doesn't use any of the guidelines published by Apple on conformity in the UI. That makes for a horrible user experience, especially when your app is made for the platform which embraces uniformity across its apps. It is not using any UI elements which the user is accustomed to, instead opting for custom-styled everything.
Now, I actually happen to agree that it's not the prettiest app. But it is a very usable app, in ways that a web browser music player is not.
I also get the impression that you're just being willfully contrary and not particularly genuine.