There are a lot of underrated Hyatt properties but I would not consider the GH Vail one of them. It is categorized as a 5 star hotel on Expedia's websites. The property is beautifully remodeled, well priced relatively speaking, and located in one of the best ski areas in America. I'm not sure how anyone could consider it underrated.
I think the Hyatt Regency Tamaya or the Hyatt Regency Chesapeake Bay would fit that answer better.