EMF/EMF 2.3/Migration Guide
There are a number of significant changes in EMF 2.3 over EMF 2.2 which require mention.
This document will expand over time to include a complete list of such issues.
The structure of Features in EMF 2.3 has changed since EMF 2.2. See EMF 2.3 New Features Migration Guide
JDOM vs. AST
JDT's JDOM API has been deprecated for many years and it does not support Java 5.0 syntax at all. As of EMF 2.3, we've migrated to use JDT's AST API instead, which supports all Java syntax. It should now be the default for the "Facade Helper Class" property in the GenModel:
So if your GenModel has this set to the older JDOMFacadeHelper, change it to the above value (or better yet, just use the circled button above to set it back to its default value which will be the above for EMF 2.3.0).
See also EMF 2.3 New and Noteworthy.