“Grey’s Anatomy” has suddenly gotten good again. After a few lackluster seasons, in which watching felt like a chore, the hospital drama is back on its game, mixing compelling medical stories with solid soap opera. In last week’s episode, Derek defied authoity and saved a co-worker’s life. This week, Arizona faced a test of ethics in a heart-tugging case of a terminally sick 10-year-old whose parents have millions to donate to the hospital. Patrick Dempsey and Jessica Capshaw gave tremendous performances. Brilliant acting raised by great writing. New characters have pumped new blood into the show as George exits, Izzie disappears and Meredith rests in a hospital bed. Kim Raver joins the cast next week. Let’s hope the upward swing continues.