Like most technologies, Datomic builds on ideas and concepts that already exist, and would find it hard to set itself apart by simply latching on to a single idea or concept. So if it were "just another" graph database and nothing more, I'd agree with you.

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