1. Consider putting preferences in their own window. This is the standard Mac behavior, and it's a little confusing to have your app do something different. You could also use the standard preferences toolbar look.
2. The artwork for your playback controls looks off. Specifically, I think the anti-aliasing of the circles looks uneven.
3. For the gear menu at the bottom left corner of the window, consider adding a little arrow like in Mail.app. That helps me know that this is a dropdown menu.
4. I had no idea what the X would do in the bottom left corner of the window the first time I pressed it.
5. Tooltips would help. You don't seem to have tooltips anywhere.
6. I was very surprised that spacebar didn't control play/pause and was even more surprised that there is no keyboard shortcut for play/pause. EDIT: It appears that spacebar does control playback. Maybe I had a focus issue before. But it would still be nice to see it in the menu. :)
7. Having "Library", "Playlists", etc. at the top of the window is interesting, but ultimately I think you'd do better with a standard look/feel. Consider using the standard selected toolbar item look. (See the preferences of almost any Mac app to see what I mean.)
8. This is very minor, but you have an extra menu item divider at the bottom of the View menu.
9. The album artwork of the currently playing song (top left corner) looks very slightly off-center. I think there's one more pixel on the right side than the left.
1. Consider putting preferences in their own window. This is the standard Mac behavior, and it's a little confusing to have your app do something different. You could also use the standard preferences toolbar look.
2. The artwork for your playback controls looks off. Specifically, I think the anti-aliasing of the circles looks uneven.
3. For the gear menu at the bottom left corner of the window, consider adding a little arrow like in Mail.app. That helps me know that this is a dropdown menu.
4. I had no idea what the X would do in the bottom left corner of the window the first time I pressed it.
5. Tooltips would help. You don't seem to have tooltips anywhere.
6. I was very surprised that spacebar didn't control play/pause and was even more surprised that there is no keyboard shortcut for play/pause. EDIT: It appears that spacebar does control playback. Maybe I had a focus issue before. But it would still be nice to see it in the menu. :)
7. Having "Library", "Playlists", etc. at the top of the window is interesting, but ultimately I think you'd do better with a standard look/feel. Consider using the standard selected toolbar item look. (See the preferences of almost any Mac app to see what I mean.)
8. This is very minor, but you have an extra menu item divider at the bottom of the View menu.
9. The album artwork of the currently playing song (top left corner) looks very slightly off-center. I think there's one more pixel on the right side than the left.
Overall, it's very impressive! Good work. :)