Banshee for Mac is not ready for primetime, and unfortunately can’t replace iTunes as your primary media player because, as it stands, the beta does not have support for iPod syncing, does not import playlists correctly, doesn’t read audio CDs and crashes frequently.

Banshee for Mac Beta 1.8.0
However, there are good things to say about Banshee. It will import your iTunes library, even correct and add metadata such as BPM and cover art automatically in the background. It supports plugins such as Last.fm, eMusic and Amazon which are killer features from my point of view. Using the Last.fm plugin you can view related artists and tracks as well as listen to your personalised radio stations.
The interface is clearly something they need to overhaul. It wouldn’t hurt to use default OSX UI elements instead of the default Gnome resources. Its simplicity however is commendable. If you’re so inclined, download it and help the developers kill some bugs. If you want to have a good alternative to iTunes, one that’s free and open-source, this is what has to be done.