The version of
Debian that
SteamOS is being built on was initially released back in
June 2013 instead of the more recent one released in
October 2013. Some people are complaining about the use of an older version, but Debian is known for how stable its releases become and this should be a good solid base. There is the option to switch from
Big Picture Mode to
GNOME to get a desktop environment which is great to have.
It looks like
Valve went for lean and stable. There is
a customized compositor based on
Xcompmgr which is lightweight. I had never heard of that compositor before so that was one of the most interesting things for me.