I started watching this movie last night and only watched the first hour. As far as I've seen the actors do not fit the historical characters mostly. The main character "Fatih Sultan Mehmet" gives a feeling of a weak man determined to destroy the Byzantium empire. He is reflected as a sick minded, obsessive person with no human feelings. If you can recall the Turkish TV series "Sultan Murad the 4th" with Cihan Unal starring as the sultan , compared to him , Sultan Mehmed character is a weakling. I think that is an insult to the actual person who is considered as one of the most heroic sultans in the Ottoman lineage. Most of the other characters also seem like they can't reflect the persona of a 15th century historical figure. They play their parts as if they are in a contemporary movie. It seems to me that the producers didn't employ serious historical consultants in the making, but they just made up stuff as they wished. If you compare the characters in this movie to a real good historical movie such as "mission" with Robert de Niro, you can see what I mean.
I think the reason behind the bad casting is in the politics in Turkey. The financiers were probably from one conservative group, the production crew an the cast were from modernists, and as a result, they didn't cast some of the actors in Turkey who would fit to some of the roles perfectly because they were affiliated with other groups. It's a pity that political wars in Turkey weakens everything from economy to film industry.
Other than these, this movie deserves praise for some good action scenes, computer generated graphics and visual effects, costumes, and set designs.