The full changelog is extensive so I’ll only cover a few highlights here
* A new render pipeline with a wealth of new features such as: 128 bits image buffer, rendering in different passes, better memory management, live render preview, tile based rendering
* Node editing systems for compositing and materials.
* The sequence editor has been completely redone: better memory management (you can now edit full movies), SPEED, chroma vectorscope and luma waveform windows, FFMPEG support for Linux.
* New Mesh tools: merging & collapse options, better select mode conversions, Loop multi-select, Path selecting, and improved Mirror modifier.
* Support for anisotropic materials.
* Improved fluid simulation which can now also handle moving obstacles.
* Better character animation tools. This includes “Custom Bones”, to create useful 3d interfaces to manipulate Armatures, and support for “Bone Layers”, allowing you to organize a rig much better.
http://www.blender.org/cms/Blender.31.0.html
