The integration with existing BI tools is a big deal. This eliminates the need to export a subset of data into a relational DB for OLAP.
Incremental refresh of cubes is super important especially when working with large data sets.
The ACL support and LDAP integration looks nice. Proper access control on top of BI data is an absolute requirement.
I don't see anywhere this is listed explicitly, but I would guess this works with data in HBASE not individual files stored in HDFS.