I think for most... we are really only ever going to be able to judge something in relation to what it is you have personally experienced, prior to.
this is true for most anything, was this car faster than the last... was this movie better than the best you've seen and so on.
the key, as already stated, is mixing in as much critical listening in your life experience as possible... including live scenarios.
my current system is NO WHERE near as good as the best system I have ever heard, that honor goes to a iMax klipsch equipped theater near me, but my system is as good as it can be.... for now.