There is a "product guide" which you can download, which gives some more information:

Query-processing enhancements

New cardinality estimator

The cardinality estimator improves the querying process and offers the following benefits:

• Consistent, predictable query performance: Different operator trees that represent the same relation have the same cardinality estimates.
• New model for better performance: Significant changes to the model result in more accurate cardinality estimates and better plan choices.
• Easier to support: The querying process separates querying into two steps, decision-making and execution. It also produces tracing output to facilitate troubleshooting.

Earlier statistics invalidation

Improvements to trigger the automatic update of statistics enable better query results, because statistics invalidation occurs earlier in SQL Server 2014. Faster and more frequent refreshes of statistics are possible because the invalidation threshold has been set to 20 percent of a single partition.

Parallel SELECT INTO

Data-loading is significantly faster because data insertion into a table can occur in parallel through the SELECT INTO operation.