I find TripAdvisor reviews are more extreme ( in both directions) than other sites. Booking.com reviews seem more objective.

I know some people threaten to post negative reviews if not given a discount!

I've been quite surprised at some of the complaints people have had about some of the hotels I've stayed in. For example, several reviews (very recent) complained about the lack of English spoken by staff at the "Golden Ring" (yes....I know, don't say anything....) in Moscow. Yet I've stayed there 3 times, twice for longish periods (more than a week, so covering shift changes etc) bracketting the complaints and found all the front-desk staff spoke virtually fluent English, with the bar staff and breakfast staff not far behind. Even the room maids on the floors I stayed on had a *few* words.

Maybe their good English came out because I intially tried to communicate in Russian (not very good at it yet)?