9 hours of new content is very good. I think I clocked Uncharted 4 in at around 12.
If you read the reviews, the main criticisms seem to stem around there not being enough innovation to gameplay or formula from Uncharted 4. Also some minor criticisms about plot and puzzles. That said other publications applauded the use of more puzzles and enjoyed the plot.
One thing is for certain; it's supposed to have that same Uncharted pacing, gameplay and beautiful visuals. Which is enough for me.
Im interested to see how ND take this franchise into the future. Perhaps a series of spin offs exploring other characters like Sully or Sam? All the while world building, growing the uncharted universe before finally revealing a new mainline entry. They're so talented, anything is possible.