Obviously the benefits of SQL Server 2014 will vary based on your specific use cases, but the features that we're finding compelling and are causing us to plan to upgrade are as follows:
- New cardinality estimator - improves the execution plans that we're seeing for some of our more complex queries, and definitely assists with the ascending key problem
- AlwaysOn enhancements - you can now have 8 readable secondary nodes rather than 4, and readable secondary replicas now allow read workloads even in the case of loss of quorum
- Delayed durability
- In-Memory OLTP
Some more details on changes in 2014 can be found at http://sqlmag.com/sql-server-2014/sql-server-2014-important-new-features and http://msdn.microsoft.com/en-us/library/bb500435(v=sql.120).aspx