The main reason I would take a family to a mega resort would be for the ski in/ski out lodging. Makes for an easier trip with less hassle than dealing with staying at a hotel 10-20 miles away from your mountain(not that I mind driving at all, but I don't have a family). Other than that, I usually prefer "smaller" mountains. It really depends on the mountain, though. I hate to paint things with such a broad stroke. I'll take Loveland/A-Basin/Red Lodge/Bridger Bowl/and many many more over Copper Mountain any day. I've had WAY more fun at those places for many of the reasons listed above. Cheap tix, low crowds, no lift lines, park right next to the lifts, great vibe, great terrain, and the list goes on and on.
However, there are a couple big resorts that I've also had a fantastic experience, namely Jackson Hole. I also want to try out a few other places, namely Big Sky, Squaw, and a couple more. It's fun to get to your destination and just hang out there for a few days without having to go anywhere. Perhaps it's the equivalent of going to Disney World with the family and staying at the park. Are there more extreme roller coasters at other amusement parks? Definitely. Are other parks cheaper? Absolutely. But DW just can't be beat for a hassle-free, all-inclusive package the whole family will enjoy, even if it is crowded and expensive. But just like Disney World, you time it right and do your research, and you can swing some pretty good deals at pretty much any resort. Again, though, I still seriously prefer the smaller independent mountains overall.