The removal of the "perpetual license" created a dichotomy in the user base. For freelance designers and small studios, the initial cost of entry was lowered (a monthly fee versus a several hundred dollar upfront cost), but the total cost of ownership increased indefinitely. The 2015 release solidified the concept that users no longer "owned" their tools but rather rented access to them.
With Adobe Illustrator CC 2015, you can: Adobe Illustrator Cc 2015 Serial Number
Which would you prefer?