
Highlights include: Improvements to the mpy format (with support for native code) and a Javascript port. But there have been many, many incremental improvements across the board - over 350 commits since v1.10 on 26th Jan. Take a look at the changelog for details.
The prebuilt downloads page already provides v1.11 builds.
Of note: Support for PyBoard D was not included in v1.11 - it's the focus for v1.12.
[Edit] Also notable: Ticket #4821 that covers the Roadmap for next release (v1.11 -> v2.0?).