Uncrowded, alpine scenery, classy town, terrain, ski school, mountain lodges
kids' ski scool at a different mountain, town and mountain separated
SV has some real strengths, and one achilles heal if you have small kids
The Town - We have skied almost every major resort in the U.S. (and some in Europre) and found Sun Valley/Ketchum to have a unique charm based on its legendary history. It is so much better than a purpose built ski-village. Ketchum (the town) is more upscale that Telluride and less show-offy than Aspen. There are enough good restaurants to try every night for a week and decent shopping. The town feels to be mostly inhabitted by retired West Coasters, but it is not an exageration to say that the avg age of the skier there is 65. The lodges on the mountain are incredibily nice (like Ritz Carltons)
Lodging - you will most likely stay at the Sun Valley Lodge which is good (not great) and is separated from town by a few miles. Catching a bus, or getting a bellman to drive you to the mountain or town is easy enough assuming your family is not skiing at two different mountains.
The biggest bummer about SV is that small children will be in ski school at Dollar mountain while anyone with an ounce of skiing ability will be at Baldy. Timing shuttle buses to drop your kids off at Dollar in the morning and then getting yourself to Baldy is a drag. Also, it is a bummer to not be able to check in with your kids during the day. We will probably not go back to SV until all of our kids are old enough to ski at Baldy. The ski school at Dollar is fantastic however, the best we have experienced. The whole mountain is dedicated to kids. My son never had more than 3 or kids in his class.
Terrain- Best for intermediates and advanced with surprisingly little for beginners. The "Green" runs would be called "Blues" at any other resort based on steepness and length. The bowls will keep advanced skiers satisfied but beware that there is no snow making in the bowl areas so you are dependant on natural snow conditions. For true experts, Jackson Hole, Alta, or Whisler would be a better choice.
I have read many complaints about the lack of snow at Sunvalley but we went at the end of January, right after SV received 2.5 ft of snow, and had great conditions. The moutain is very well maintained through snow-making and grooming. The scenery from the summit is fantastic.
Overall a great place and more unique than anyplace in Colorado or Utah but taking shuttle buses from the lodge to town and two different ski mountains got tiresome with kids.