"Well written" IS the common denominator for good TV.
(That may have been the secret to the success of Two and a Half Men.
Since I hated Charlie, I avoided watching Two and a Half Men, then ultimately became addicted to it; in spite of Charlie. The writing above all, but the cast is fabulous; Conchata Ferrell, Holland Taylor, Jon Cryer, Angus T Jones, Marin Hinkle, and Jane Lynch. It's a shame, I can't watch it now.