When the show first started out, during the David E. Kelly/Jeffery Geiger era, it was pretty good. It had a dynamic cast, and exciting characters. It primarily dealt with issues of law, and the life of the Jeffery Geiger, a troubled cardiologist, whose wife had drowned his baby during a schizophrenic episode. The most fascinating aspect of the show was "will Jeffery Geiger go crazy.'
During the show's second season, David E. Kelly decided to leave. The lawyer, Alan Birch was killed off, and Jeffery Geiger took a `leave of absence.' At this point, many of the David E. Kelly and Mandy Patinkin fans decided to give up, saying that the show was no longer as good. With the loss of Alan Birch, the `law aspect' of the show disappeared. However others prefer the `post DEK period.' The show became more of an ensemble, with a great mix of characters. There was quiet Aaron Shutt, who was a good supporting character, feminist Kate Austin, tough Billy Kronk (who ended up in a relationship with his polar opposite, Diane Grad), lothario Danny Nyland and fatherly Philip Watters. Later on Jack McNeil, an orthopedist with a gambling addiction, and Rocky Caroll, a no nonsense doctor were added. This mix of characters did a good job carrying the show for the next two seasons. These seasons were some of the best television I have ever seen. They included storylines involving Danny Nyland and Billy Kronk helping out an inner city youth `doctor.' Kate Austin dealing with her difficult ex husband, and precocious daughter.
But, by the fourth season, things began to crumble. Danny Nyland (my favorite character), was written out, without a clear reason. Diane and Billy became engaged, married and then parents within one season! Because of this Billy began to loose the edge that made his character interesting. But the biggest nail in the coffin was the fact that Aaron's character had changed overnight! After an aneurysm, he went from being a neurosurgeon, to a psychiatrist. The show attempted to show the more `emotional' side of Aaron, but we had already seen that various times beforehand. Instead of developing the character, they changed him overnight into a `caring sensitive guys,' who attempts to help boys whose brothers had committed suicide. To replace Aaron they added a new neurosurgeon, Lisa Catera (named after a car commercial 'lease a catera). While the character would not have been that bad had they added her a season or two beforehand, the fact that she was `Aaron's replacement' and that she was getting too many storylines, gave the audience the impression that she was being shoved down our throats. Because of this, she became one of the shows most loathed characters.
By the fifth season, things began to deteriorate completely. Philip Watters was turned from a fatherly figure, into a man whose regretted having an affair with his wife. This was horrible. Two seasons beforehand he revealed to Billy Kronk, that he woke up with and went to bed with the same women for 30 years, and in the episode after Alan's death, felt guilty about starting a relationship with another women. They did a lame storyline with Kate Austin going into space...and added yet ANOTHER annoying character played by Eric Stoltz, who was diagnosing people using his 6th sense. By this point, many frustrated fans began quitting. It clearly should have been the end of the show, but for some odd reason, CBS gave it `a second chance.' In the final episode of that season, they suddenly fired four major characters, Kate Austin, Billy Kronk, Dennis Hancock, and Lisa Catera. As a longtime fan of the show, I would have preferred seeing what happened to them, despite their deterioration 
The sixth season was an attempt to bring the show back to its roots. While Jeffery Geiger was brought back, he wasn't the same character he was first season. He lost his `will he lose it edge.' He became the `evil one' who fired the rest of the cast. In addition to Geiger, they had three new female doctors running around the hospital. It was very difficult to bond to these characters, especially in the 'absence' of the ones from the previous season. David E. Kelly, was supposed to stay at the helm, but abandoned the show, prompting Jeffery Geiger, to leave the show quickly, this time to take care of his daughter (who had been aged into an annoying 6 year old, a stark contrast to Kate Austin's daughter). By the time the show was done, it had deteriorated once again. In the final episodes of the show, the hospital was purchased by an eccentric millionaire played by James Garner. The last episode was a sad reminder of what the show had become. It dealt with a paralyzed millionaire(who did something in computers) making a pair of `fake hands' so he could move again.