Before there was "Grey's Anatomy," there was "ER," the original, long-running hospital drama full of breakout stars, memorable storylines, and a revolving door of cast members. The premise itself is pretty straightforward. It follows the ups and downs of the doctors and nurses working a busy emergency department. "ER" is probably the closest analog you'll find to "Grey's Anatomy," with many very similar elements: epic but sort-of forbidden romance, hospital power struggles, shocking medical cases, dramatic "event" episodes, and much more. It's also a super-long runner like "Grey's," spanning 15 seasons. In fact, it's the second-longest medical drama in TV history, second only to (you guessed it) "Grey's."