Castle, "The Fifth Bullet": Face doesn't ring a bell

"Castle" is one of those shows I watch from time to time but rarely write about, in part because it usually takes me a few days to get all the way through an episode. (It's something I tend to put on for a few minutes in between other things.) But I watched all of last night's episode - which paired Nathan Fillion with fellow strapping Whedon alum Marc Blucas, and threw in Anne Dudek and the ambiguous ethnicity of Carlo Rota for good measure, as the show has become quite good at guest casting - and thought I'd take the temperature of the room on the state of the series.

The ratings have been better this season, thanks in part to Jay Leno, and it seems to me that the chemistry between Fillion and Stana Katic is stronger and less forced than at the start of the series. (Or perhaps I've just gotten used to them.) I still don't love the mysteries, but they've gotten better at coming up with the sort of hooks that would intrigue a guy like Castle - what mystery writer wouldn't want to work a case involving amnesia? - and the plotting is mostly an excuse to let Castle annoy Beckett for an hour.

If you're watching, what do you think? Any areas where you feel the show could improve itself? Or do you just like Fillion enough that the rest is window dressing?