In a way, I wish all WP plugins were like this: uncomplicated, unobtrusive, with just a few sensible features. Of course that's not practical, there's a place for full-featured do-everything plugins, but looking under the hood of this baby is a thing of beauty! I mean: customize away! This thing is ready to do what you want it to do...speaking as one who loves to twiddle with code and CSS. I didn't take me an hour to figure out how it worked and what I needed to do to make if fit the site.
If you like to customize, this is the one...if you want lots of features and the ability to customize without coding, we'll there's other plugins for that, like MP3-jPlayer.
This one is getting 5 stars for restraint and elegance--and for being just the thing I needed. By the way, it works in Firefox, don't worry, jPlayer is solid.