Have it and love it. In order to watch a decent amount you do need a subscription to something. Netflix, hulu plus, amazon, etc. We have netflix and amazon prime but for us, amazon prime has some trouble with streaming. Others don't seem to have the same problem so it's probably a hardware issue. We also have a lifetime subscription to playon which lets us watch shows on network sites and also youtube and a few others. Playon is a little more glitchy because it connects to your computer first, and then your internet. The other channels connect directly to internet. Keep in mind also that hulu plus, even though it costs, has commercials during the shows.
Installation is easy. You just hook it up to your tv (we used an HDMI cable) and plug it in to the wall, and then connect it to your network using the remote control. You do need a decent wireless internet connection but ours is skimpy at around 2.5 mbps (on a good day) and I have no problems watching a movie on netflix. Some models have an ethernet port that lets you do a wired connection to your router.
eta: we also still have directv because dh doesn't really like navigating on the roku, plus we like watching current shows on the satellite channels.