Recs.
Updated
Alienware's SteamOS version of the Alpha. This machine is pretty capable at running your games that are compatible with Linux at 1080p quality. It contains some hardware that, can be argued, is better than the current gen consoles. It has some upgradability in certain parts like the RAM, storage, and can even run Windows if installed. The big downside is that neither the motherboard nor the GPU can be upgraded since both are integrated together. Overall, it's a small form factor that can fit almost anywhere in your home and be sitting proudly next to your other consoles.
SpecsUpdate
Pros
Pro The R2 model may have an amplifier port
There have been posts claiming the R2 version of this system does support an amplifier port like the Alpha R2 but is covered by the plastic casing. It can be cut through but that will void the warranty. You could also take off the chassis entirely and use the port that way but that will look ugly and can attract dust. If you don't mind cutting through the plastic or remove the case to use the amplifier port and get yourself a desktop quality GPU then by all means.
Pro A reasonable price point
The R1 models are now on sale and can cost $300 for a base model I3 and $500 for the top of the line I7. The R2 versions, although a bit more expensive, still make it in a range that people can afford the machine to be in their homes alongside their Xbox Ones, Playstation 4s, and Nintendo Switches.
Pro R2 variants have reasonable GPUs
When you get away from the base model of the R2 variant and pay higher for the other I3 with 1 terabyte, the I5, or the I7, you're dealing with a GTX 960 that packs a bigger punch than the base model's custom GTX 860M. It can last you for awhile until you need to upgrade which is possible with the supposed hidden amplifier port.
Cons
Con Steam controller dongle is weak
There is a hidden port where the Steam Controller dongle is placed in the machine, this obstructed eye of sight gives issue with the connection to the wireless controller when used past 10 feet. Luckily the dongle can be moved to a front USB port on the machine, which does help.
Con GPU can not be replaced
Sadly there is no way to swap GPUs (like a regular tower PC) and so will detract from the longevity of this device.