There is little 'chemistry' between the two of them like there is Castle and there was in Fringe (for example). Sleepy Hollow has much more and they aren't even an 'item'.
It's the players, not the script, even Jane would have some chemistry if Katic played Lisbon, it's great fun watching Fillion sweat when Katic turns up the heat. Castle is adult humor, Mentalist just another buddy cop show and one that won't be remembered long after its gone.
I absolutely loved tonight's episode. However, I sure didn't like the preview for next week. I hope they don't make the mistake of killing off a main character with four episodes to go just to add "drama" to the end of the run. I for one, like happy endings.