Naturally, there are quite a bit of additions and changes that have been documented. For those that might be using this as a 'daily driver' OS, Google has also listed the known issues with the latest build of Android M.
The system Messenger app crashes on the 64-bit emulator.
After updating to Developer Preview 2, Contacts sync experiences intermittent issues. The workaround is to clear and re-sync Contact Storage data after update. To clear data, go to Settings > Apps > Show system > Contacts Storage. Select "Storage" and then Clear data.
In YouTube app, it's not possible to share a video. The share window is blank.
Android For Work Profile setup is not working properly, so you won't be able to create a new Work Profile after you update. As a workaround, make sure to create the Work Profiles you need in Developer Preview 1 before updating to Developer Preview 2.
Issues specific to MPZ79N on Nexus Player:
Bluetooth share crashes after clearing data. Please do not clear Bluetooth share data, otherwise you will need to Factory Reset your device
There are issues with remote control connectivity. Remote can drop from Bluetooth pairing when left idle.
Movies show black screen with some ANRs on exiting the video.
In YouTube app, lower-resolution videos have a green bar at the top and some color-ghosting
For a complete list of reported issues, please refer to the open issues list on the Developer Preview issue tracker.
For those that will be installing the preview, be sure to check out the full details of known issues from Google's developer page. If you encounter any bugs in the preview you can submit bugs here. It is highly recommended to install the OS only if you capable of reverting back to your previous OS. Currently, Android M 'Developer Preview 2' will support the Nexus 5, 6, 9 and Nexus Player.