What if Matt Damon's The Martian returned to Earth 20 years later & found that the Planet has been devastated?

I really was wondering if those robots were real or CGI, so that's good.
Also the cinematography is beautiful. 

Halfway through the movie I asked myself what had happened until now, but I couldn't say. It's really slow & draggy. 
I didn't invest in these characters. 

A rare miss by Tom Hanks.