So I'm 2 days late to the party, but I got my Controller and Steam Link last Friday.
As of right now Steam is required to use the controller as a mouse/kb replacement, I haven't tried any games without Steam on.
The controller itself is comfortable in my hands and it pretty straightforward in games that support gamepads to begin with. The real challenge is setting up profiles for games that don't have controller support out of the box.
I've played a few games with it (over my Stream Link)
South Park - Stick of Truth: Works great, takes some getting used to.
Deadpool - Works pretty alright, can't tell if the controller isn't up to snuff or the game doesn't control all that well to begin with.
Team Fortress 2 - I didn't set up the controller, my experience was dreadful, I will experiment more.
Witcher 2 - Yeah, the tutorial has a tab button, I have no clue what button was bound to tab. Will experiment more.
Binding of Isaac Rebirth: Works pretty decently, although using the trackpad was awkward, I'm still getting used to the controller.
Civilization V - I was able to found my first settlement, pick out my first productions, research and take my first turn. Op success.
I may have messed around with another game or two, I don't remember. My opinion is that it's a good start for something new and different. Obviously there is a learning curve. If you don't have $50 to waste don't buy the controller. You may not like it.
Now the Steam Link, which I thought would be something neat turned out to be my favorite part of the order. Steam Link is a STB, but it's barely bigger than the average smartphone. It comes with an HDMI cable, short ethernet cable and power cord. Interestingly, the power cord also comes with three different power adapters for use in different countries.
Set up was easy and once I linked my Steam Link to my Steam account I was able to stream right then and there. The interface is Big Picture Mode obviously, streaming was good I noticed lag only on one game, I can't remember exactly which one it was though. You can install and remove games from your PC through the link, using the controller you can also turn off the link, the PC or reboot the PC. It's pretty rad. I'm looking forward to playing with it some more when I get home from work.
If anyone has any other questions, I'll check back when I remember and try to answer them.