Don't buy a Steam Machine - The Verge.
The official Steam Machines run SteamOS, which is basically Linux with Steam’s Big Picture Mode. Even though Valve is working to bring more games to Linux, most popular titles aren’t available for it yet, and there’s really no reliable way to predict which games will be supported in the future. Of the top 10 games you can buy on Steam right now, only one, the Fallout Classic Collection, works on SteamOS. There’s no Grand Theft Auto 5, or Skyrim, or DayZ. Hell, you can’t even play games that are compatible with Linux but aren’t on Steam, which includes Blizzard’s popular catalog. If you care about playing anything relatively new and popular, the Xbox One, PS4, Wii, and Windows-based PCs are all clearly superior options. And games aren’t the only compatibility problem. If Valve and HTC’s virtual reality headset is anything like the Oculus Rift, it’ll need powerful hardware, and it’s possible lower-end Steam Machines won’t support it.