Sometimes I just wonder that hard it would be to made compact (padding,button size etc small as possible for finger, not default hildon) two column player where on left side is folder view and on the right side file view. Basket to one cornet where you can drag and drop files to current playlist. Bottom seekbar,volumebar and default media player button play,pause,forward etc. Additionally EQ and Gapless playback. This would be IMO good core for folder base media player.

For examples in windows desktop look for foobar2000 and 1by1. Those are pretty minimalistic and very functional players. God I hate so much wasted pixels :| in so many apps.

.edit
Ideally best would be to combain best features from minimalistic and big apps. I would say that midnight commander kind of approach is nice but it should be pimped.