I really loved this series for the first few years, but when Arturo left, it started the slide to mediocrity. It accelerated when Wade and Quinn left, to the point it was rambling nonsense. Don't know the reasoning for the actors leaving, but it did ruin it. Perhaps it lost some direction as there was little purpose to each episode other than surviving long enough to slide to the next world. Unlike Quantum Leap, which had a similar premise, but it's purpose was to fix things in each episode.
