Here's a small sampling of what was written up. The consensus seems to be that Clinton won, Sanders impacted the content of what was discussed, and the neither of the other three candidates - Chafee, O'Malley, or Webb - did enough to distinguish themselves.
- Slate: Yes, Bernie Won Every Poll on the Internet. Hillary Still Won the Debate.
- National Journal: Why Bernie Did Better Than the Pundits Thought.
- The Atlantic: Hillary Clinton's Surprisingly Smooth Debate.
Vox offers a round up of different takes on it here: 2015 Democratic debate on CNN.