Thanks again for all the suggestions. I have tried calibrating the various picture modes (Movie, Standard, Dynamic, Natural) and playing with the color tones within those settings (Warm 2, Warm 1, Standard, Cool) and the picture invariably has a British look to it, and not the glossier American image quality that I'm used to.
I'm really stumped. I'm not a videophile and I'm usually content to make only a few basic changes to the presets, but this TV just doesn't agree with me. I don't know if it's a dud or if it's supposed to look this way.