I'd argue that tripadvsor.com would be more useful to me than the direct hotel website as I'd see more neutral outlook of the hotel compared to the hotels website itself. I know, the reviews are not 100% neutral given neutral experiences usually don't end up in reviews - only really positive or negative do but it's still useful than not having any opinions which would be the case on hotels website.

Also, the travel websites give the important details, amenities, nearby attractions, restaurants, public transit in the same format across all the hotels so I don't have to fiddle with each and every travel's website in a different way based on what their UX designer decided to do. Also, wayyy more photos on travel websites.

Disclosure - I used to work at TripAdvisor.