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Its very much advanced version and contains excessive features than 4.0. The following link will show you the features and phones of jelly beans OS
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:
And an overview of the changes in Android from version to version: