A question was asked on the Solr Users mailing list on how to assess a comprehensive list of Solr features. It is an interesting question, as Solr is like a balloon being blown up. It is expanding in all directions. It is unlikely that one person will be able to comprehend all the features before the next release adds some extra. Solr is definitely not a slow tortoise when it comes to competing with hares. Especially when it is the tortoise that decides in which direction the goal lies.
Still, there must be a way to approach that state of knowledge, however asymptotically. Here would be mine, which comes from the practice of writing a Solr book as well as numerous Solr training materials.