We have a reliable source (two, in fact) telling us that the first over-the-air updates to Android Lollipop will come not to the Nexus 4 or 5, but to the Nexus 7 (2012), Nexus 7 (2013 Wi-Fi), and Nexus 10. Why? Because they're all Wi-Fi devices - supposedly hardware with cellular data will have to wait a bit longer to get the OTA, meaning the Nexus 4, 5, and 2013 Nexus 7 with LTE will be stuck a bit longer waiting for the L update. The updates for the Wi-Fi devices will arrive on November 3rd.
We're confident in our sources and the quality of the information provided on this. What's new in Lollipop? A lot, and you can check out Google's official changelog right here.