Article link. Announced at CES.
I think this is rather ridiculous, IF the specs and prices are correct.
So basically, you are spending the same as an Xbox One w/ kinnect.
You get Steam OS - so all those benefits of cheaper games, sales and such in a console experience with Steam Big Picture - alongside the ability to go to a Linux desktop (Debian based, which is good) and still get that PC experience. Yes, I'm aware consoles have browsers and such, but its just not the same as a PC desktop environment, especially with Linux, extremely flexible and awesomesauce. It's also possible to get those console exclusives working on PC, but that might take some know-how, and not sure about the difference in methods between Windows and Linux.
As for specs - doesn't mention exact CPU or how much ram (which I can only assume would be 8gb), besides that very similar to next gen consoles. On par, maybe a bit ahead of PS4, I think. Xbox One GPU is definitely behind.
So basically, yes, €100 more than PS4, but is just worth it. Can't build those PC specs for that price on your own without some serious skimping. And that ability to upgrade parts if that's your thing. Probably will be even more models.
As for the Steam controller, I don't really know much about it, not really interested. If it actually works well, it could be quite amazing to get that console feel of a controller with a mouses accuracy. (Or so they have said)