There are a lot of things to like about 12c. In no particular order:
In-Memory Database Option: This is a paid option but it essentially allows you to run your RDBMS as a dual relational/columnar database.
Multitenant: Now, instead of having multiple sets of metadata and processes being used by each instance on a machine, container databases use a single set of administrative processes for each installation.
Analytic Capabilities: Too many to list here, but lots of powerful additions to the SQL language, including modeling and pattern matching.
HA Features: Application continuity is a great addition to making HA architectures much more flexible, as is Data Guard Far Sync.
Compression: Oracle can compress your data on disk by rules you set based on how frequently the data is accessed. Think of it as partitioned compression.
Data Redaction: New abilities to mask data in a dynamic way so that only authorized users and applications can see certain sensitive data. Great if you're moving to the cloud.
We're able to reduce hardware costs by colocating and coalescing previously separate, dedicated database instances into fewer stacks. The addition of new analytic functions means that we're less reliant on NoSQL solutions for reporting and can even connect directly to Hadoop and MongoDB to work with data in other silos.