What reviewers don't seem to understand is that this kind of machine is WAY too powerful to be a steam machine (as are the reference steam machines Valve shipped, which is kinda funny). This is a gaming PC in a small form factor with some UI rice and a controller. What's the difference, you ask? Steam Machines, when they debut, will be targeting the lower end of the market (sub $500) in order to directly compete with the consoles their UI is designed to compete with. If Valve wanted to compete with Microsoft in the high-end space, they would made a desktop environment the default and not put so much emphasis on Big Screen mode, and instead focused on performance and an integrated, smarter Wine wrapper.
In order to compete with consoles price-wise, you have to dodge the Windows tax. That's what the SteamOS is designed to do, and it succeeds it enables OEMs to build systems with a controller included that beat all next-gen platforms at sub $500 price points. Nothing else matters, because SteamOS can't compete at the mid- or high-end of the market - it simply lacks the compatibility of Windows.