Don't have Roku 3, but have Roku angry bird and I really like my roku.
I have smart tv, smart blu player, ps3, wii u all of which can stream content but roku is easiest to use. Change TV input and it is there, no need to wait. The UI is nice. I use it mainly for Amazon prime and Crunchyroll. Amazon's prime app is nice there, much better than my panasonic TV. (had Netflix for awhile. don't know if there is any change to app now. ).
big negative is no official youtube yet but it is hinted that it is coming back soon. (I use videobuzz which isn't bad, but for youtube, I mostly use my laptop with widi for ease of use).
I don't watch any of the free channels, so as far as cable replacement, dunno, but I think between amazon prime, netflix, hulu, there should be enough content to keep you busy.
