Received my Roku 4 yesterday, do not have a 4K TV yet ( waiting for all the HDMI/HDR stuff to finish baking, remembering how I was burnt on two HD component only TV sets that will only work with a cable box).
Quick view point on the 4, damn fast on playing anything, hit play it is ready to go, had my Roku 3 ( that is going downstairs to replace my Roku stick) hooked up at the same time thru my receiver on the same TV input, the picture is better for some reason on Netflix ( using Jessica Jones playing at the same time on both the 3 and 4), a lot sharper, do not know why, on the 3 a little murky maybe, on the 4 super sharp.