I think there was still plenty of material for two or even three great seasons, but if it's a choice between getting this solid, extremely satisfying ending and the uh-oh that was the last season of Castle, then it's a no-brainer - rather have five brilliant seasons than six great, seventh good-ish and the last barely "okay"...

And I agree - they managed pretty well with the shortened season. Obviously there were a few moments that felt a bit rushed, but nothing serious that would take away from the enjoyment of the series. Really, they did a fantastic job with it and I'm very proud and happy for them.

I wouldn't really want a POI spinoff, but I wonder if they have any plans for a different show in the future; with a different premise... I think I'd definitely check it out.