Where to find the official Cyanogenmod release notes? Where are the official release notes for Cyanogenmod, in particular the 9.1 release? I wasn't able to find them.
Did you check with the official changelog site? Or the XDA thread on 9.1? The latter mentions http://cm-kang.appspot.com/anzu/ics for the changelog. And then there's this page where you even can filter changes by devices (probably the best source to check).

If you need more details: All that from page 1 of a simple Google search for cyanogenmod changelog "9.1" (&lt;- hint! ;) )

To the first (and explicit) question: If there were any new features? That probably very much depends on your device. So using the last changelog source I mentioned, filtering by the device you want to know this about, you will be able to answer your question. As I don't know your device, I can't ;)