Cyanogen is dead – welcome Lineage OS, on my Samsung Galaxy S3 i9300.
I have installed todays nightly zip using TWRP 3.0.2-2 recovery. Did a TWRP backup before followed by a factory default wipe (internal memory not affected) . Then flashed the nightly zip. No issues with that nor during initial setup. Got all my apps installed from fdroid and a few out of the TWRP backup, no Google stuff for me. Calendar, contacts and tasks imported via webDAV, nice and easy. There are obviously no backgrounds in this initial nightly, got that from my backup too. Also, there is no root by default.
The announced root.zip seems to be not yet available for download.
Let´s see how Lineage behaves on the SGS3 i9300. Hopefully much better than the last CM13 I had installed. That was a PITA.
Root is available for download https://download.lineageos.org/extras. For Samsung Galaxy S3 i9300 download addonsu-arm64-signed.zip then flash in recovery mode.