CKAN allows you to pick and choose which features you want to use for your data portal. There are over 60 different extensions, all of which can be independently added in any configuration you choose. Anyone can build new extensions and contribute.
Google analytics extension for monitoring traffic on your data portal over time and tracking number of downloads per resource on the datasets themselves.
QA extension which checks the data download links and provides a broken link report by publisher. This also includes the 5 stars of openness assessment report on datasets.
Geospatial This extension contains plugins that add geospatial capabilities to CKAN