Oracle 12c has helped us lot by cutting down limitations that we were fetching currently in traditional RDBMS.
12c has functionality of plugging databases (PDBs), where we can form master slave architecture and run multiple DB from single master. Cool isn't it?
Second cool thing, it supports JSON. which is quite helpful if you have application with REST architecture.
I don't see there is something to dislike about 12c. Yes, cost is definitely one of the factor where any organization needs to evaluate if it's helping them go positive or not. Because cost of 12c itself and device on which it runs are relative. Which definitely is high. But, again as i said, it would be totally organizations call.
Like is said above 12c has pluggable feature. But, again in order to use it effectively, you need lot of preparation. For ex:
All cluster DB must be configured to handle the resource requirements in accordance with PDBs that you are going to manage, else you will have to shutdown to reconfigure and restart the Cluster DB and all the PDBs. Additionally, you need to keep in mind small things, e.g. container, and all PDBs, should be running on same character set. Hence, it's better to switch to Unicode.
12c is definitely a beast which needs proper care to keep running smoothly. Of course, all the beast do. ;)
I would sum benefits to 3's. Scalability, Security and Stability. Pluggable database of course has helped lot. It's quite a state of art. It has helped lot in managing & reducing time and effort for database upgrades, backup, recovery, etc.