How masterful were the grand masters?

The National Gallery today “unveiled” (actually I think it just “opened”) its Cezanne exhibition, marking the centenary of the master's death. This led me to think two things.

Firstly, what skill do you need to be able to exhibit to be described 100 years later as a “master”? Secondly, why would anybody want an event to mark (or celebrate) their death?

What did people of the mid 1800's actually think of young Paul? Did they think that his paintings were “...a bit splodgy”; “...lacked detail” and were generally devoid of facial detail because “...he couldn't really capture expressions”? Or did they stand in awe of his artistry?

Given that his work was generally ignored during his lifetime, it appears that the former are more likely to represent the views of the time.

Thankfully, the fact that my work is also largely ignored, possibly means that in 2146, I could be considered an absolute genius.