I use this thing every day. A couple of things you might not know:
MLB.tv Premium allows you to watch most out-of-market baseball games. No, you can't tune into anything that will be available to you via cable, but it's been a great to watch my beloved Dodgers from Oakland.
This box is the best way to watch Amazon VOD. Yes, you can get some content via Amazon Prime, but it's just as easy to buy TV shows on a per-episode basis, or rent movies for $3 or $4. I must have all of Archer, bought via Amazon, usually available the night after airdate.
The slowness of the interface will slowly drive you crazy. It's a low power chip, so getting into the video can be a hassle, and interacting with the box will strain your patience.
To sum up, the great channels are: Netflix, Amazon, Hulu Plus, MLB, NHL, Pandora, among many others. Happy Roku'ing!