  Gunrock is the winner of the 2018 Amazon Alexa Prize, as evaluated by
coherence and engagement from both real users and Amazon-selected expert
conversationalists. We focus on understanding complex sentences and having
in-depth conversations in open domains. In this paper, we introduce some
innovative system designs and related validation analysis. Overall, we found
that users produce longer sentences to Gunrock, which are directly related to
users' engagement (e.g., ratings, number of turns). Additionally, users'
backstory queries about Gunrock are positively correlated to user satisfaction.
Finally, we found dialog flows that interleave facts and personal opinions and
stories lead to better user satisfaction.
