Ok, so superuser app installed from superboot, but I didn't have root access. To fix this, I powered down the phone, connected to my computer, then booted into the bootloader (vol up + down + pwr). After this I double clicked the install-superboot-windows. The Nexus will then show the Google screen with the lock at the bottom. The screen will hang - leave it be for 2-3 minutes. Pull battery, reboot and you should be good to go.