I bought the Roku a few months back. I don't have cable and wanted to watch a few shows here and there.It's pretty simple to use, but to me it doesn't feel like a parent proof device.
The UI is split up into "Channels" which are essentially different applications that grab video listings. The most popular one is netflix. It should be noted that you cannot browse netflix from the Roku (yet). Your instant queue is displayed on the top row, and then various other options are displayed below it. There are groups like "Recently Watched", "Critically Acclaimed Movies From The 80s", "Dark Documentaries", and then recommendations, one from netflix and a few others based on things you've just watched, and a search feature. All of these, except the instant queue, search and netflix recommendations appear to be random.
I have had one technical problem with the netflix channel. From what I can gather, when netflix goes down and you try to access the channel it can lock the channel up, making all videos you try to watch unavailable. The only solution was a factory reset.
There are some other good channels as well, MLB.tv, Nasa.tv (haven't had much success), Khan Academy, TED Talks, and a few others. There is a way to stream videos from your PC but it's a bit of a nightmare.
All in all, it's a great little device, and I'm happy with the purchase but it may be one of those "you get what you pay for" things, but I've never seen any of the other devices. If you need more help feel free to email.