My housemate and I BLOODY LOVE Grey's Anatomy. It's the crack cocaine of medical dramas and came very highly recommended before I took the plunge with season 1 about six months ago.
(Disclaimer: I don't advocate drug use)
The writers have you emotionally invested from the offset and each series ends fantastically - either on a massive cliffhanger (a la series 5 - oh god) or just after a major event.
It helps that the male characters are smokin' hot, of course. I've claimed McSteamy, HM likes Karev but Avery's come on the scene now, who I think might trump them both!
This is us re-watching the series 6 finale. Having already watched it, I came home earlier to find HM weeping - really weeping, halfway through. I did warn her it was bad!
We decided a second viewing would help us 'come to terms' with the events just passed.