I've always had a problem with the Debra character from a plausibility perspective -- supposedly smart, competent cop who doesn't have a clue that her own brother has been on a six-year killing binge (not to mention the ex bf) -- yet aside from the title it's the only one I consider indispensable. Having said that, I get a bad feeling about this season's Dex-Deb arc and where it will lead...
Agree this season has been the weakest by far. (It's been downhill since Season 2 IMO.) The plot swings from boring (Capt. Matthews subplot) to ridiculous (just one obvious question: what does Quinn need to do to get fired?) The acting is still strong, but the writers have run out of ideas. Time to either close shop or clean house if there is to be a Season 7.