Very poor
This app is probably ok if you have 10 or so songs on your device. Browsing by artist or album doesnt actually let you choose a song, it just shuffles everything from that artist or album. Looking for a specific song requires you to browse the entire song list on your device, so be prepared to have to type out the song name in search.
If you use iTunes Match there is no way to tell what songs are actually available. As it lists everything thats in the cloud, even though it cant play the songs.
Its really feature crippled compared to the stock music app. Gestures are nice, I guess, but theyre not enough to make up for everything this app cant do (or requires more work to do) compared to the stock app.
The Tom Canuck about
iMusic - The Perfect Music Player - Listen to Free Music Without Even Touching Your Screen, v3.1.1