I don't think this device and a Steam Machine (just a PC with a badge on it) will be in the same realm of competition. This would most likely compete with the Ouya, where the Steam Machine would compete with the 5th gen consoles.
FireTV is built on Android and has a real controller for gaming. It won't compete with Steam Machines for high-end games but there's certainly enough hardware to pull off some great games and apps.
Well this is running android and Steam Machine is running full fledged linux(debian?). Comparing a set top box to a personal computer isn't really fair.
As for the gaming capabilities, it'll be interesting to see if they can compete with Steam Machine.