Going on a 7 day vacation to new, exciting places every year! That's the biggest problem
The real answer probably depends on "you" and how you view your ownership and the property you own.
If you own a great timeshare property (and can trade it) and like to vacation, you probably don't view any issue as negative or disadvantage. The only thing I can think of might be the maintenance fee... but its like any fee --- divide it by 52 weeks and its not much to go on a 7 day vacation.
I've got friends how complain or say this/that... but when you think about it... it comes down to liking your timeshare property. (because I don't have the complaint's they had).
PS. I own in Maui and Vail.