well finally got round to watching it disliked most of season 4 so stopped watching it half way thought the series. episodes 20, 21 and 23 werent to bad and the finale was ok thought they dealt with castle and becket getting together really well. the reason i stopped watching was it really started to take its self too seriously gone are the banter and funny situations of series 2 now its a cop show all about the crimes. and this Johanna becket thing is really beginning to drag now.
they need to step up their writting from the lazy uninspired writing of season 4 or they could be in danger of not getting a season 6
Good thing for you then; I think they said they'd be returning to the lighter side for the new season. Still be a few drama episodes, but it's going to be a breather season.