Beta 1 Release Notes apply to Beta 2, additionally:

Improved Pattern Detection

• Expression Trees: Multiple levels of nesting are now supported better

Misc

• CreateCecilObjectModel: extension method to help plugin writers porting their plugins to ILSpy 4.0
• IAmbience API revived: If you want to nicely print type names or member signatures in C# style, you can now use CSharpAmbience
• "Open containing folder" and "Open command line here" added to Assembly tree nodes.

Improvements & Bugfixes

• Local functions: Code is no longer hidden if local functions are used in the code, as long as they're not decompled correctly. Note that this might still lead to compile errors, if anonymous types or lambdas are used in the local functions.