The best description is in History of Modern Tibet 1913-1951 by Melvin Goldstein. He is very knowledgeable and unbiased.

First of all when you try to make judgement on society that you don't know try to collect all information available. Beginning with harsh high altitude climate and low fertility of soils and proceeding further.

Goldstein in details describe "exploitation", "serfdom" and monastic system existed in Tibet before Chinese invasion. It was not an ideal society but it was distinctive society which majority (I can say overwhelming majority) of people found satisfactory.

Tragedy of Tibet was its location between geopolitical giants and decline of Mongol power in Central Asia and of course Tibet had no chances to preserve its unique culture in the same way as indigenous American civilizations could not preserve their culture and freedom under European onslaught.