Some encodes are rushed and you get glitches and the quality can be poor at times although it only affects TV not films. To be honest, a small glitch and poor gradients I can live with, I'm not paying for these shows so can't really complain.
Spoiler:Highlight the text in the black area to see it.Example being in the first episode of GoT when Sam is walking through the snow, looks absolutely awful but still more than watchable.
HDMI cable it digital, either works or it doesn't work. Get the cheapest ones you can. I've had two fail and they were both the more expensive ones that the shop were selling for £15 a cable but threw them in with the TV. My other cables which I have bought for £2-3 are working great.