I posted a little while ago that I've fallen in love with this show. Nothing has changed. Every episode makes me like it more.
The greatest twist this episode was discovering that Kate has actually been a Castle fan for years and years. The bantering between Kate and Castle is fantastic, but discovering this adds a whole new level to it.
Castle is obviously a tiny bit smitten with Kate and we get that feel of tension that she might like him a little more than she lets on. I applaud the writers for adding this bit of backstory. As enjoyable as it is, the friction between them could begin to get a little stale. By bringing this facet of Beckett's character into sight it adds a dimension that makes me want to go back and watch earlier episodes with this in mind.
Like when Kate goes to his book reading and signing. She's got to be loving the fact that she gets to hear him read his new book and, if she's like any other book lover I know, dying to get her hands on a copy, but she has to play it cool.
Add to that the fact that he's actually basing a new character on her...Up until now it's seemed like she is mainly putting up with him. Knowing that she is a HUGE Castle fan means that she is a better actress than Castle would ever suspect.
What interesting plotlines this opens up. I can't wait to see how it all plays out.