David/Maddie, Sam/Diane, Jim/Pam - I've had enough of the whole 'will they or won't they thing' and Castle doesn't need to go down this road. Get them together and figure it out from there. I'd even be ok if they break up, but enough with the teasing. Castle is a very immature person, and Kate is ultra serious so I can't see it ultimately working out, but either way it would give the show a nice dimension.
The mystery itself was pretty generic, and could have been slotted into any number of procedurals. I was trying to figure out how the British guy (who I think slipped briefly into an Australian accent) was the murderer, but they got me on that one.