From the GitHub release page:

2.0.0 is getting close to ready! We just need folks to test all of their projects with this new code and report back if they find bugs. Thanks to those who found bugs and those who contributed code.

DO NOT use this release if all you want to do is try CircuitPython. 1.0.0 is much better for playing around.

Here are the changes since Beta 1:

• Update to MicroPython 1.9.2.
• Introduce a nvm.ByteArray to provide limited byte storage even when the file system is read-only.
• Explicitly load frozen modules from the .frozen python path instead of the empty path implicitly.
• digitalio.DigitalInOut now errors on extra arguments thanks to @deshipu for finding the issue.
• atmel-samd: microcontroller.cpu.temperature support added.
• atmel-samd: CircuitPlayground Express. NeoPixel library is now frozen in.
• atmel-samd: Fix PulseIn.resume. Thanks @asherlie and @brentru for finding the issue.
• atmel-samd: Fix PB07 pin ADC mapping. Thanks to @cledic for reporting the issue.
• atmel-samd: Trinket M0 now has named SPI pins at @deshipu‘s request.
• esp8266: Fixed file system issues.

Moving from 1.0.0 to 2.0.0 is not a perfect process. There are a few things that break when doing so.

• mpy files compatible with 1.0.0 are NOT compatible with 2.0.0 because MicroPython changed the format. A 2.0.0 bundle is available here. (Its built by changing the branch of circuitpython in the bundle repo before building it.)
• uos is replaced by os, storage and multiterminal
• urandom is replaced by random

This release is based on MicroPython 1.9.2. Support upstream MicroPython by purchasing a PyBoard (from Adafruit here).

Have a Feather M0 Express, Metro M0 Express, Gemma M0, Trinket M0 or Circuit Playground Express? Download a .uf2 and follow these instructions. To install our libraries simply download the bundle for your release and copy the lib folder onto your CIRCUITPY drive.

To install on legacy boards, download a .bin file and follow the guide here for M0 and here for ESP8266.