They should have ended it in Season 2, but the ratings were good and they kept going. As other people said, the writer's strike killed Season 3, and 4 was just pathetic at times. They could have done a 2 hr made for tv movie to wrap up the story line better than an entire season.
They had to have a season 2. But after that yeah should have ended. Season 1 is one of my favorite tv series seasons ever