I thought it was good. The whole shift of tone was radically different from the other episodes before it. Castle really didn't like being on the other side of the law. It was really touching that Beckett still believed him.
I thought the way that Espisito learned of Beckett/Castle was anti-climatic. Castle does have a flip side. It's kind of nice that Castle (the show) can change from the doom type episodes to the light/comedic ones.