vSphere 5.1: What's New
What's New in vSphere 5.1
Introduction to VMware vSphere Data Protection
Introduction to VMware vSphere Replication
Introduction to VMware 5.1 - Performance
Introduction to VMware 5.1 - Storage
Introduction to VMware 5.1 - Platform
Introduction to VMware 5.1 - Networking
Hope these will give you a good idea on the changes.
As for the editions and add on, the same editions that are in vSphere 5 are still here which includes Essential, Essential Plus, Standard, Enterprise and Enterprise Plus.
What has been added is Standard with Operations Management. This edition adds in vCenter Operations Suite Advanced for active monitoring and capacity monitoring and vCenter Protect Standard for patching. This edition is very useful for customer starting on a small virtualization project while still able to provide a good active monitoring tool and patching systems all in one package. For the vCenter Operations Management Suite, it is still licensed by per pack of 25 VMs. However for this vSphere edition, all VMs licensed in this suite will be protected and not restricted by the any number of VMs. However this only applies to VMs that are hosted and licensed on vSphere Standard with Operations Management and no VMs on other licenses.
You will see what is available for all vSphere Editions from here. Do ignore the entitlement portion as that is for kits purchase and customer are allowed only to purchase one kit per site to be used.