Here I go writing about another series: Castle
It is a police investigation series which started in 2009. But just as for The Mentalist, the action revolves around one non-police character, armed with a sky-high ego. In this case, it is a successful mystery author who goes by the name of Richard Castle. After deciding to kill he's star hero, he strikes a slightly writer's block. That's when he meets his new muse Detective Kate Beckett, and pulls up some strings to follow her around for her cases.
The essence of the investigations is not extremely developed: some interrogations, few forensic scenes (but I don't miss that), a chase or two; and the solution of the cases usually comes on the spur of the moment.
But what holds everything together is the chemistry between Castle and Beckett, their small confrontations being delightful.
So if you enjoy slightly immature, egocentric, narcissistic, stubborn and big-mouthed characters, this is your thing.