We stayed in the Holiday Inn Bloomsbury this summer, and it was literally 50% off the rate for any similar hotel we could find anywhere by booking through hotwire. ($150/night*10 nights=me booking through hotwire)
Anyway, we figured it was a typical city Holiday Inn, so I was quite satisfied considering the price. It was listed as 3.5*, which I'm not sure if I'd quite go that high, but it was certaintly a 3* facility. For us we mainly wanted a bed, a clean room, and a good location, so it worked for us.
On the other hand, we booked a 3* in Barcelona that I would have rated as MAYBE a 2*. It was an old converted apartment building and the rooms were quite dirty. It was only for one night while we waited for a cruise ship, but I wouldn't have wanted to stay there any longer.
For me, in the future, I will probably book directly with hotel in non-english speaking countries, but will continue to check hotwire for Canada/US/UK, especially when the savings are so significant, as they seem to be in London.
Michael