I have to say that I just think the question is flawed from the get go. Everything is relative and what sounds great now will sound dated in short order - it's just the way things are.
Dated does not necessarily mean bad - quite frankly most of my favorite albums would sound dated by most standards, but none the less they are my favorites. Old does not equal Bad and New does not equal Good in many cases.
Perhaps I'm getting old, but I miss the days of dynamics in recordings - a difference between the softest passages and the loudest. Perhaps that is the thing that makes things sound dated, but regardless, it's all still relative.