Good timing! The day after you post your question there is a review of 4.2 on ars technica.  It's an improvement, but not as great of an improvement as the jump from 2.3 to 4.0 was. 

Here is the ars review:

http://arstechnica.com/gadgets/2012/11/review-android-4-2-is-a-sweeter-t...

And an overview of the changes in Android from version to version:

http://socialcompare.com/en/comparison/android-versions-comparison