Disenchantment was the first thing that popped into my head. For a Matt Groening animated series, the colors are incredibly dull. The humor and overall story also left me disappointed.
I watched the first episode of one of those period shows, I think Barbarian. I couldn't get past how impeccably clean all the peasants looked. They were wearing the right clothing, but it looked fresh out of the dryer. I wish more shows would take the time to dirty up the sets and actors, deadwood was great at this.