This penultimate season of Six Feet Under continues further down the darkly disturbing path so evident in the third season. To be sure, the signature--and ultimately undefinable--blend of tragic mishap with tripped-out comic eccentricity that has stamped the series from its debut remains pervasive. It's the concentration of the mix that has changed. Leavening moments seem less organic, much as the bizarre death sequences that open each episode often turn out to be rather contrived preludes to the ensuing thematic obsessions. Which isn't to say season 4 lacks the delightfully memorable quirkiness fans have grown to expect. Recurring incidents of fecal revenge bring tensions to the surface between Ruth (Frances Conroy) and her new husband George (James Cromwell), in turn leading to young intern Arthur's resignation (Rainn Wilson's spot-on characterization is so enjoyable that his self-imposed exile from the Fisher nest early in the season is a real loss). Ruth meanwhile hooks up again briefly with the irrepressible Bettina (Kathy Bates) for an excursion south of the border.