Reviewed in the United States on November 3, 2017
Fantastic product so far! After the first week, we bought a second one for a family member.
First thing: Before you buy, understand what content is free and what is not. Second, in case it's not obvious, the Roku operates over your wifi and internet connection. You have to have an internet connection that is fast enough to stream video. If you can't stream video on your mobile (via wifi) or PC, you won't be able to stream it on the Roku either.
Subscription content: Anything that you have to pay for elsewhere (like Netflix, Amazon, Hulu, network TV streaming, etc), you'll still have to have those same subscriptions. But the Roku allows you to access all of those subscriptions (the ones you're paying for) from a single device on your TV, with a nice interface that nearly anyone can use, even if they're technology-illiterate. Worst case, if you get lost somewhere, just press the Home button. (But keep in mind, each 'channel' on Roku is an app written by the individual content provider, so some are a little more complicated than others. I suspect for marketing reasons, it's not always obvious on some of the network TV channels which content is free versus paid until you try to play it. But you'll always be prompted before paying for anything, and you can add a pin-number to prevent accidental purchases).
Ad-supported content: There is a lot of ad-supported content, just like watching free over-the-air (OTA) TV stations. For network TV (ABC, NBC, CBS, CW, etc), check each network's website to see what shows you can watch for free directly on their website, and that's generally what you'll be able to watch on Roku, too. After all, the 'channels' on Roku are apps written by each network. For many networks, the free content includes the last 3 to 5 episodes of things that are currently airing, with content being made available a week after the original broadcast date. This is comes in handy if you miss an episode or two of over-the-air TV. Some of the networks also offer free 'throwback' content, where you can watch an entire series of an older show. And there are a few channels like pluto.tv and tubi.tv that provide a wide assortment of ad-supported movies and TV shows. Again, check their corresponding websites to see what content they currently have, and that's what you'll get on Roku. The ones mentioned above offer some relatively recent content, in addition to a lot of older and slightly-older content.
Free, without ads: Mostly, you'll find that the ad-free content is extremely old... lots of black-and-white TV and movies, some early color TV/movies, etc. For those who don't like much of what's on TV these days, there's a lot of classy and classic stuff here. And, of course, a lot of b- and c-grade stuff you've never heard of.
This newest version of the Roku Express ("5X more powerful") has a very smooth interface, with good response from the remote. Video startup is extremely fast if you have decent internet speed. I tested on a relative's 6mbps DSL internet, and buffering times were never uncomfortable. On my faster internet (100mbps), videos either start instantly, or take no more than about 1 or 2 seconds of buffering.
The remote control is great -- simple, strong signal, good range. It's infrared-based, so you have to be in the same room (why would you want to be out of the room??). I generally don't even have to point the remote at the Roku box, because the infrared is strong enough to reflect off of the ceiling or walls and still work. Just be sure your Roku box's front side is unobscured and pointing toward the room. They provide a sticky-tape strip to stick the box somewhere convenient, like the side or top of your TV or media cabinet. The provided HDMI cable is only 2 feet long, though, so it does have to be relatively close to the TV. But you could use a different HDMI cable if you need the remote to be a little farther away. One feature I love about the remote is that pressing the Home button will turn on your TV and switch to the Roku's HDMI input, assuming your TV supports this (I have a Samsung TV which is supported, and a TCL TV which apparently wasn't).
You can also use the Roku app on your mobile to control the Roku via wifi. In addition to providing an interface that looks pretty similar to the physical remote, you can also browse for other content while something is already playing. It fact, it's quite a bit easier to navigate if you're searching for something specific, since the physical remote requires using an on-screen keyboard where you select each letter and click OK (normally, I'm not searching for something specific on the physical remote, so it's not a problem). The app also has a headphone feature, which I'm guessing allows you to listen directly from your mobile instead of via the TV... great for watching at night when others are sleeping. Note, the Roku app is NOT designed to watch Roku content directly on your mobile. It simply lets you select the content to watch on the TV.
Overall, it's a great experience. My only subscription at the moment is Amazon prime, which doesn't have a lot of content that I really want to watch (sorry, Amazon! I have Prime mostly for the shipping), so I use the Roku mostly for ad-supported TV and movies, and there's more than enough to keep me busy for a long time.