I got a midrange 50" Panasonic Plasmsa a couple of years ago and I'm not all that satisfied with it. It says that the picture is THX certified. The black level fluctuates depending on the content on the screen (and it's a sudden shift). There is a lot of color banding in gradients. There is some buzz, especially when mostly showing white. If there is something high contrast in the image, like blinds, it is ghosted across the width of the screen. It doesn't have pixel-perfect sharpness. The viewing angles beat any LCD, though.
I hate the LED hype... they market it like it is a major panel type like Plasma, LCD or OLED, when it's just another kind of backlight for an LCD.
OLED has issues too. They have a non-standard color gamut. Brightness adjustment can be more difficult.