I'm sure others will kick in with more than I can offer, but imo everybody needs to ski A Basin at least once.
If you're in to amenities and glitz, AB is as far from that as you can get, but the skiing is fantastic, and they don't get the masses that the other summit co resorts get. They have plenty of intermediate and advanced terrain available, as well as expert terrain if you're up to it.
Outside of A Basin? Keystone is right down the road maybe 15 minutes away. Copper and Breck are a short drive away as well. For planning purposes, if you plan to hit a few resorts, be aware of the fact that you can ski the Vail resorts (Vail, BC, Breck, Keystone) and A Basin off the same ticket if you purchase your tickets through Vail's Peak program.