Crowds, expensive (parking!), difficult to navigate on mountain, super resorty
Vail is an experience unto itself. It is huge and has vast amounts of terrain with tons of expert stuff. But it is usually crowded, which exasperates the difficulty in getting around on the mountain to access all that terrain. It can take over an hour to get from one side of the mountain to the other, longer in "ski lock." plus it is super resorty and insanely expensive. $20 for parking for crying out loud!
But use a pass, go with a car full of buddies on a powder Wednesday and it'll be the best snow experience you'll ever have!