Philip Howard of Bloor Research has another great post on graph databases. He discusses the proposition that graph databases will have a bigger impact on the database landscape than Hadoop or its competitors.
The point to understand about graph databases, especially when it comes to analytics, is that the more nodes you have in your graph then the richer the environment becomes and the more information you can get out of it.
He offers a great concise summary of the differences between Hadoop and Neo4j:
Speaking of Neo4j, one other essential difference between Hadoop and its ilk and graph databases is that the former is primarily seen as an environment for processing queries whereas at least some graph databases can be used for transaction processing. Neo4j, for example, supports ACID-compliant transactions and XA-compliant two-phase commit. So Neo4j might be better equated with a NewSQL database, except that it can also handle significant query processing.
Read the full article.