Eight years ago, we discovered "The Mentalist" in the form of two early DVDs in a charity shop in France. We watched one and didn't watch the other, as we had to get back to England to start from series 1, episode 1 (back in the LoveFilm days). I'm 40% through re-watching all 151 episodes. There was never a single episode I could fault in any way (and I'm a very picky watcher).
The individual episode plots have nice twists, the detail of which I seem to have forgotten in the intervening years, so they are just thoroughly pleasing to watch again. I'm already looking forward to eight years from now, when I can start them all yet again.
As a caveat, do not be put off by series 1, episode 1 (the pilot). If any episode had a fault, it would be this one, where they introduced too many of the later plot arcs than can comfortably fit into 45 minutes.
THis is a must watch series. One you just want to watch all at once, although my wife said it was a bit repetitive.
Nice easy viewing. Intelligent and interesting but a bit too easy/convenient at times.