For gaming, it's just ok. The main problem is that on most OSes, the speaker and headphone sound doesn't work, but the HDMI sound output to a monitor is fine. I've heard the speakers work in SUSE, but I haven't tried it yet.
Steam downloads were slower for some reason in Kubuntu. Game streaming from my desktop to the deck looked terrible and had lots of lag. I'm guessing it was an issue with the network drivers.
Steam has to be running in order for all the buttons and trackpads to work. You can still use them outside of Steam, as long as it's running in the background. But if Steam isn't running at all, you'll only have basic keyboard/mouse/x-box style joystick functions.
Long story short, I still use SteamOS for gaming. I use Kubuntu for experimental stuff, because I don't know anything about Arch.