So, I would give this 3.5/5 . I enjoyed it overall. The sites were very interesting, and its shot beautifully. Hancock is a good narrator and I learned some cool stuff.
The problem is how reliant the entire thing is on Hancock's narration. His theory is largely speculative, lacking any real evidence besides convergent oral traditions which seem to be cherry picked to support his argument. Usually, documentaries like these have more input from experts. He interviews people - some credible, some not - about sites, but they get very little airtime.
Lastly, love Keanu Reaves... but why the HELL is he in this thing? Bizarre.