It's sad that this is a new concept for so many people in the software industry, considering that graphs are one of the core data structures taught about in CS.
However, Datomic puts together a whole host of other concepts - data immutability and all its resulting benefits; separation of query, storage, write, coordination (with carefully considered trade-offs); Datalog-based querying in place of SQL; in-app access to data with a great solution for the string concatenation hell that we've all gone through trying to juggle our SQL, and the list goes on.
I don't think any of these individually make Datomic special, but collectively? IMHO, outstanding!
Edit: For those interested, we have a new Datomic Community on G+ where we have collected a number of links to Datomic resources and videos: https://plus.google.com/communities/109115177403359845949