Recently while exploring CRM 2015, when rest of the world was talking about all kind of new features added to CRM 2015, one of my friend pointed to a small change made to Subject field on Case form which sound bit weird and not at all user friendly for data entry. The change was “Subject lookup is changed to Option Set type field”. Not really, but yes it is again a new complex field that you cannot customize something similar to full name field.
Consider a scenario where I have a CSR creating a Case while on Phone Call with the customer. With CRM 2011, CSR can directly type into the Subject lookup and the value will get auto populated, but with CRM 2015 option set kind field CSR will have to manually drill down to Root node à parent node à Child node and more dipper based on the Subject tree complexity.