This has so far been the most fun and satisfying experience I have had when it comes to adopting a system for your everyday work. The tagline says it all, 'Simple, Fast, Scalable'. I have worked on datasets with billions of records in computing scenarios as complex as would make a Hadoop developer cringe. Granted that it uses a declarative language, a paradigm which is not the most familiar to programmers in 2013, and the system has its own non-standard quirks, it is still a platform which makes you feel at ease.
I give this a five star rating! My personal experience has been that I was able to download the HPCC VM image and get started with loading and transforming data in a few minutes. Thanks to their central deployment tool, setting up a 3 node Ubuntu cluster was really simple. The inherent parallelism and data flow nature of the powerful ECL language removes the worry about trying to parallelize my jobs, as was the case in my experience with Hadoop MapReduce. In fact, I have to say ECL is somewhat similar to SQL from the perspective both are declarative data programming languages. So if you are a good SQL developer, ECL should be a breeze to understand and use. It is a mature platform and provides for a data delivery engine together with a data transformation and linking system. The main advantages over other alternatives are the real-time delivery of data queries and the extremely powerful ECL language programming model.