It's become quite chic to dismiss Susan Sontag as outdated and rather silly.
In serious fields, there are seminal works which we don't dismiss. We might update terminology and notation, we acknowledge that certain aspects turned out to be wrong. We might note that updated ideas have rendered some of the material moot, that we now think about certain things in a different way. Some things might even become untrue as the world changes.
Nobody uses Newton's formulations of Calculus any more, but neither do we dismiss him. We respect and, honestly, revere him a little. Even though his notation sucked, and he was a lunatic, the ugly reality is that he got a lot of the ideas right.
Sontag seems be dismissed mainly because her writing is 40+ years old.
She got a lot of stuff right, it turns out, and a lot of the stuff she got right isn't going anyplace until the human brain starts to work differently. She was also a pompous ass, and wasn't right about everything. So it goes.
My favorite is when someone disses Sontag, and then proceeds to parrot ideas that appeared, if not first then quite early, in Sontag's writing. To be blunt, it's pretty hard to say much about photography that is both interesting and true without slamming into a Sontag idea almost immediately.
So, rather than peeing on Sontag, perhaps critics of photography should recognize her work as what it is: Seminal, with all the good and bad that implies.