The Jelly Bean version of Google Music has been ported and modified to work with Ice Cream Sandwich ROMs. I’ve currently only confirmed it to work on the HTC EVO 4G LTE and the HTC EVO 3D running ICS, but i should probably work with any Android 4.0.x based ROM.
It appears they might have fixed the long-running problem with the wrong album art popping up along with a bit of cosmetic surgery to make some things look better, and the widget has been improved to show album art along with a thumbs up/down, pause, fast forward. There’s also a setting that seems to indicate this was ported from the Nexus Q, and leads you to a Play Store page for a setup tool for it, but this was useless for my phone.
To install, simply download the APK and choose install. I required no root tools, uninstalling of Play Music, nor ADB usage in order to get the application to install. Your mileage may vary depending on if Google Music was originally installed as a system app in your ROM or not.
For the full shipped Jelly Bean effect, you’ll probably need to install the new slim Jelly Bean Roboto font, although that’s not required for use.