I enjoyed it immensely. Did you all catch that the guy who was Castle's biggest fan, getting autograph at the beginning was Jonathan Frakes? I confess, I only caught it because of the TV Guide article. But it was fun to see him.
Frakes' exact line was "I'm your Number One
fan." Obviously that phrasing wasn't by accident, and I had to rewind it a couple of times before my wife got it.
And Castle comments under his breath "How far they fall" as Frakes walks away. I wonder if that was intended as a comment on how Paramount is now favoring TOS over TNG?
Also, what's the reason Firefly was only mentioned as "that Joss Whedon show" when there were so many nods to Firefly in the episode?