I second Donnyb in everything. He´s right about the terrain, it´s the steepest in South America, the off-piste accesed by the Marte chairlift offers literaly hundreds of chutes, bowls and couloirs. If you want to hike, the Cerro Martin and Torrecillas are 40 - 60 minutes away from the Iris surface lift.
September is the best time to visit Las Lenas. I believe the best time is right after the "Santa Rosa" snowfall, usually from August 30 to September 4 or so. Las Lenas is about timing: snowstorms and wind can have the resort closed for a few days.
I believe Las Lenas has an excellent avalanche control system. In fact, last season they brought two army cannons to work on avalanche control besides the Gasex and Cadex. This mountain has many avalanche prone areas, but even when you have to wait a couple of days till the hole mountain is open you´ll be safe. They won´t let you ski or ride anything untill there´s no avalanche risk.
Due to "El Nino" we are expecting huge snowfalls this season. The Pacific gets warmer sending us tons of snow.
As I was working in Las Lenas in ´97 (an El Nino year) we got an early snowstorm that gave us 3 metres of snow in 4 days!! That was crazy, but the skiing was the best I´ve ever had.
If you ask me, and as Donnyb said, if you´re a serious skier, head down to Las Lenas this winter!
I´ll be in Las Lenas this season. Maybe we can hook up for some powder day in the Andes.