I liked it, but here are my issues...
1) I can understand a little historical fiction, but to take real people who existed and completely twist their history is detrimental to all those who watch it and don't know any better. Like watching Disney's Pocahontas. A Christian army invading Mongolia at the end of the series? Really?
2) I felt the characters become more "modernized" as the show went on. They became more relatable in ways that I can only assume were due to changes in writing style. For example, Kublai seemed much more approachable as the series went on and not so feared and dangerous (unless you are a five-year old).
3) The story arc of Marco losing the trust of his captors only to gain it back by some wild stroke of fortune was getting old.
4) We all have access to free porn online now. It's not necessary to have all the sex/nudity scenes cluttering up the show (perhaps a Weinstein requirement).