Caesar's critics were unhappy with how much power he amassed and for other things such as the fact that he distributed land among the poor. Aristocratic Romans did not like Caesar, and other Roman politicians resented his power.
Very few leaders have had the unanimous support of their people, and Julius Caesar was no exception. Though he was an extremely successful military leader and politician — consolidating power, defeating Roman enemies and gaining territory abroad — he had his detractors. Of course, the bad things about Caesar are a matter of perception. He was extremely unpopular among aristocrats due to some of his policies, which favored the poor and therefore angered wealthy Romans. Caesar's success at gaining and consolidating power also led some to suspect he was trying to become a king in Rome: this is something that was not supported by the political system and public opinion of the time.