A great article with lots of information on new features in Ruby 2.0:

Keyword arguments

Symbol array literals

Refinements

Module#prepend

Binding unbound methods to any object

Binary search for Array and Range

Enumerable#lazy

RDoc Markdown support

Use warn like puts

Logger compatible syslog interface

TracePoint

Asynchronous Thread interrupt handling

Garbage collection improvements

Optimized backtrace

Zlib streaming support

Default UTF-8 encoding

True thread local variables

Net::HTTP performance improvements

…

Link: Ruby 2.0.0 in Detail via globaldev.co.uk