I dont have the book with me anymore so I am writing from memory but the short version is that the act simply did not give enough powers to the indians and in some cases didnt even return powers that they had before they were taken due to world war 1.

Common complaints included the following-

The number of elected members in the councils was a small majority, most of the seats were reserved by the british for their lackeys and puppets like the petty kings and zamindars

The councils also had little to no powers. most of the decision making powers were retained by the central government and there were no guarantees that the laws and rules passed by the councils would even be enacted.

Source: India's Struggle for independence -Bipin Chandra