First, let me say that I love this show, it's my second favorite current show (the first being Warehouse 13, though it's off until the summer). And I get that this show isn't Law & Order, it's more about the play between Castle and Beckett and Castle and Alexis than it is about the cases.
That said, am I the only one that is getting more and more disappointed by the cases, though? Week after week, figuring out who the bad guy is before Castle and Beckett do is getting easier and easier. I didn't think too much of it when Ray Wise turned out to be the killer (he is the Devil, after all), but this week, in "The Mistress Always Spanks Twice", the killer had not even uttered a line, he/she (I'm trying to avoid spoiling anyone who hasn't seen the episode yet)was only on screen for a couple of seconds, and I knew he/she did it. Which wouldn't have bothered me (like I said, I get this isn't Law & Order, I get that it's really about the relationships), but then this was an episode where it seemed like the writers gave us an extra dose of red herring suspects. So it appears like the writers would like for us to be guessing whodunnit all the way up to the end, which means they're trying to put at least some emphasis on the case ... but then they make it so easy to figure out who did it that a blind man could solve the murder before Castle and Beckett.
It's just disappointing that they seem to want us to care about the cases, but then make them so very easy to solve that it defeats the purpose. They could learn a thing or two from the people who wrote Murder She Wrote or Matlock, two crime shows that also were done with a lighter energy and were more about the characters and the relationships than the actual cases, but which still managed to write interesting cases that were at least a little challenging for the viewer to solve.