The reason for rating it two stars is very clear. If you have seen Br Chopra's Mahabharat, then you'll automatically feel that which representation was better. And if you have just read real Mahabharat's book you will too notice the difference. The reasons for rating it two stars are:-
1. Fake scenes which are not mentioned in the book of Mahabharat- India has a beautiful history,India is a religious country where once gods lived. So,at any costs,it's history shouldn't be changed.
2. Character's role- In this representation, characters are not at all able to play thier role. In case of historical serials,actors have to Play the roles on thier lives! The acting should be done in such a way that it's viewers must feel that it's realistic. Here,the one who is playing the role of Duryodhan, Dhrithrashtra and Bhishma is spoiling there characters by faking too much of voice!
3. Extra and fake events- As I mentioned in 1st point.
4. Wrong character to a wrong person- I think here no explanation should be given as it is Automatically seen!
5. Dialogues- absolutely wrong dialogues at some scenes! The way of speaking and expressing too matters.
.....So this were some reliable and valid reasons given by me. Graphics Alone doesn't matter. There are 100s of things which can be done to make a serial better.
.. Thank You
..Jai shree Krishna