All the enhancements around extended events are pretty excellent. I'm also enamored of the distributed replay mechanism (although I wish it worked with extended events too). Availability Groups are extremely awesome. Mirroring finally done right.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning