Chabi was a favorite of mine and so was Hundred Eyes. Kublai was great, though I agree with whoever said it was disappointing to get less of him in the latter episodes.
I watched the first few episodes with a friend who absolutely couldn't stand Prince Jingim, but I got where he was coming from. He was irritated at his father favoring Marco, who he (naturally) viewed as an interloper. Also, Remy Hii is pretty, so that may have helped too.
As for Marco, I totally agree that he was the least interesting character. They really didn't need him to tell the overall story. That said, I didn't mind him or his portrayer.
Finally, I'm going to miss Sidao. I thought he was a great antagonist for Kublai.