The smaller knob to the right of the radio display with the musical note is what is used for the audio settings. Push in on the knob to step through the menus, spin the knob to change the settings.
The Driver Information Center is moved from the radio to the dash. It is a two line white dot matrix display, similar to the radio in clarity and resolution. I really like the newer displays better as they show a lot more, including the XM radio information (the older radios SUCK for this). It's also a much better display for the presets on the newer system.
The automatic climate controls are pretty similar but the manual climate controls are a lot different between the two series.
For the steering wheel controls, the button on the older series that selects the radio presets (marked '1-6') is replaced by a phone button so you can use OnStar without pushing the rear view mirror buttons. There is also a radio mute button on the steering wheel that is not on the older series. Oh, and Bluetooth was an available option in the new series!
Finally something to note is that the newer series totally changed the command interface to all the electronics. The older series uses what's called '11-bit LAN' while the newer series uses '29-bit LAN' and accessories made for one are not compatible with the other - though pretty much all the aftermarket accessories (iPod adapters for example) are available in both versions.