There is no doc that has those differences you will have to comapre the 2.2 release guide to the 3.0
The 3.0 has a new GUI, compliance is working and EOX/PSIRT also working
Its more stable than 2.2 as well
http://www.cisco.com/c/en/us/td/docs/net_mgmt/prime/infrastructure/3-0/user/guide/pi_ug.html
http://www.cisco.com/c/en/us/td/docs/net_mgmt/prime/infrastructure/2-2/user/guide/pi_ug.html