Solr 2014: A Year in Review by Anshum Gupta.
If you aren’t already excited about Solr 5, targeted for alter this month, perhaps these section headings from Anshum’s post will capture your interest:
Usability – Ease of use and management
SolrCloud and Collection APIs
Scalability and optimizations
CursorMark: Distributed deep paging
TTL: Auto-expiration for documents
Distributed Pivot Faceting
Query Parsers
Distributed IDF
Solr Scale Toolkit
Testing
No more war
Solr 5
Community
That is a lot of improvement for a single year! See Anshum’s post and you will be excited about Solr 5 too!