10 has Association expressions [1], which are a huge language addition (and long overdue). Seems there is some synchrony with Erlang on that front!
The features I'm most excited about in 10 (disclosure: my team is working on some of these):
[2] String, XML, file templating
[3] Hands-free machine learning
[4] Entity and EntityValue: semantic "hooks" to represent real world entities
[5] Dataset, a general data modelling and query framework.
Also, DateObject, TimeObject, interaction with external processes, multiple undo, a large number of updated data sources, the ExternalService "meta-api", device connections, time series stuff, GeoGraphics, and a long list of no less worthy features.
[1] http://reference.wolfram.com/language/guide/Associations.htm...
[2] http://reference.wolfram.com/language/guide/WorkingWithTempl...
[3] http://reference.wolfram.com/language/guide/MachineLearning....