Vail/Eagle, Steamboat Springs Yampa Valley Hayden Airport are very difficult approaches, however they are not nearly as difficult as Aspen's approach.
I'm sure you all heard the deadly Gulfstream crash in Aspen while it was decending to land.
When you decend, you are unbelievably close to the ground, and to the right of you are the mountains which are also very close, if you don't keep a steady decent, it can be fatal. Also, the wind shears in Aspen can flip a plane over, there is a lot of turbulence while landing in Aspen and is only for experienced pilots.
They recently recieved permission from the FAA to install an advanced landing system aid, and additional lights to improve safety.
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran