Alongside improvements in the interface, the Moodle 2.0 Quiz has some changes to the quiz reports very powerful features enabling advanced analysis of student responses. In brief:
Graphs have been added to some reports to give us a quick overview of the results.
The Responses report lets you download all students' answers to all questions. (This used to be an "optional extra" in Moodle a non-standard, contributed report, but proved so popular it is now added to the main release.
The new Statistics report, giving much more detailed information, has replaced the old Item Analysis report. More information on this is available here: http://docs.moodle.org/en/Development:Quiz_item_analysis_calculations