Ron, I have been and all skiing in the sumer is awesome!! The main thing you need to know about skiing in the Andes is that they generally get very large but infrequent storms. Most storm days the winds are so high that the lifts are closed. Storms can last for several days. Almost all the skiing at the three resorts at Valle Nevado is above the tree line, so you can pretty much forget about tree skiing. When visibility is poor it is very hard to get your bearings. I would reccomend that you bring two sets of skis. A powder oriented ski and a carver. You can arrive when there hasn't been snow in weeks and it may not snow the whole time. The rental shop was not great as I remember it.
Valle Nevado has some awesome terrain!! In general the slopes are quite empty and the on piste and off piste experience is pretty sweet. The other two resorts have decent terrain as well and they are worth skiing over to. It's a nominal additional fee to add them to your pass for a day.
The altitude is high and as I remember you will be sleeping at close to 10,000 feet. If you have any issues with sleep at higher altitude or altitude sickness make sure you bring whatever you might need.
The food is pretty good and the room plans generally come with 3 meals included.
If you are flying into Santiago, I would get a car in advance to take you to the resort. It's a solid 2:00-2:30 hour drive and the last hour is on a sharp switchback mountain road where the elevavtion change is easily 6000-7000 feet.
The ski director at the resort is American and from killington. He is a very nice guy and I have forgotten his name. You should go out of your way to meet him. He was very helpful to us on our trip. He knows the mountain top to bottom and he understands what we as Americans are looking for. If you are lucky enough to have some fresh snow, I would have him set you up with a guide to show you some great off piste terrain and show you around the mountain. If you are skiing groomers I don't think you need to spend the money because the groomed terrain is pretty self explanatory.
Lastly, HYDRATE!!! The elevation is higher than we are used to and it is very, very dry!!! All of us got a little sick the last day solely due to hydration.
Enjoy the trip. You will have a blast!! If I can help further, send me a PM.