Well first there is his role in the conquest of Gaul which brought in massive amount of treasure and revenue for not just the Roman state but for Caesar and his Legions. Romans generals typically shared the spoils of war with their men which in turn increased their loyalty to their General. During and immediately after his conquest of Gaul, Caesar did an excellent job of cementing Roman hegemony in Gaul (this will be important for later). He did this by pitting some Gallic tribes against eachother, making alliances diplomatically with some, and subjugating by force with others. The result was a wealthy province that was too divided to unite in opposition to Roman rule. By the way, one event that opened the window for Rome to move into Gaul was an appeal by the Gallic tribe, the Aedui, who appealed to Rome for help against an invading German army. Caesar defeated these people and then consolidated Roman authority in Gaul.

While this was going on, the Roman Republic was struggling. The senate had been increasingly corrupt with the bribery of voters, the intimidation of juries, and sometimes even murder coming to play a large role in Roman politics. The three most powerful men in Rome were Pompey, Crassus, and Caesar. Each of these men maneuvered for position and sought to gain power for themselves. For a little while the three formed an uneasy form of checks and balances where the power of the three would prevent one from becoming too powerful. This fell apart when Crassus was killed in a failed campaign against the Parthians which left Caesar and Pompey to compete for power in a rivalry that would lead to civil war. Caesar won the bloody civil war and assumed full control of Rome. The senate at this pint was pretty much a figurehead with very little real power. The senate granted Caesar dictatorship for ten years and gave him a triumph of unprecedented expense. When he assumed his role as dictator, he found Italy in chaos. The civil war had proved to be devastating to a state that had seen a century of Oligarchic misrule and revolution (The Roman arisocracy had pushed out the individual Roman agricultural class that had formed the backbone of Roman manpower and at the start of Caesar's fight with Pompey, Rome still hadn't recovered form the Social Wars a few decades prior). Thousand of estates had been ruined and the provinces had been exhausted of their wealth by corruption and civil war. At this time he faced opposition from the aristocracy called him a usurper and opposed his rule. Including the spreading of rumors that Caesar planned to move the capital to Alexandria and name Cleopatra as Queen of Rome with himself as emperor. Caesar subordinated the senate almost to an advisory role, increased its membership from 600 to 900 including 400 of his own appointees. Many of these were Roman businessmen and many were elites form provinces throughout the rest of Italy and other provinces as well. The patricians predictably didn't like that Gallic chieftains were now in the senate and had government positions. He played an active role as judge in Roman courts and proposed an orderly codification of Roman law. He also distributed land to both the poor and to veterans form his legions. He passed laws to prevent a reconcentration of property ownership by the Patricians. He sent thousands of jobless plebians to work in the colonies including Carthage, Greece, and Iberia (Spain). He also put people to work by spending 160,000,000 sesterces in a building program in Rome. He expanded his Keynesian policies to the rest of Italy and the provinces. These programs included the restoration of temples, the building of roads, the draining of the lake Fucinus and the Pontine marshes which would have removed the threat of malaria to Rome. A lot of these policies were done with the cooperation of non-patrician businessmen and remember that the patrician class resented his rule especially since his land redistribution policies hurt them the most. What probably was the most resented of his undertakings was his plans to make the freemen of Italy (non-Roman Italians) equal citizens with the Roman citizens. In 49 B.C. he enfranchised Gaul and in 44 B.C. he drew up a municipal charter to equalize all Italians with Roman citizenship. He also took control over the appointment of provincial governors from the senate and reduced provincial taxes. He made plans to restore Carthage with new colonists to inhabit the land. Now, I've just realized that I've written a shitload of text here and I'm sorry so I'll move quick. Caesar was assassinated by the senate and specifically, the patricians who opposed his policies which both increased his political power at the expense of theirs and decreased their wealth by his support and cooperation with non-patrician businessmen and with his pro-plebeian policies.

Caesar was clearly a dictator and was jockeying to make himself emperor but at the same time he held the Roman empire together after years of devastating civil war had ravaged the countryside and drained the treasury. He helped the poor and unemployed with his policies. He did not live to see many of his plans complete since he was assassinated a few months after he had been declared dictator for life. His adopted nephew Augustus, after another civil war, would assume power in Rome and see many of his plans through.

Caesar's problem was not one of substance, but one of form. He openly disrespected the Senate, in one famous instance by refusing to stand when the Senate entered a meeting with him. In his lecture series with The Great Courses, Garrett G. Fagan uses a phrase I think encapsulates the different styles between Caesar and Augustus. "Caesar never met an honor he didn't like"

Caesar was known for not refusing the honors proposed to him by his supporters in the Senate, whereas Augustus made a great show of refusing certain honors, and ruled not as Dictator but merely as the Princeps, or 'First Citizen'. Caesar ruled directly and openly, and had used the power of the mob to get his agenda across. This caused a great amount of anger on the part of the conservative Senators, most notably Cato the Younger. If the Senate refused to work with Caesar, he would ignore and bypass them without a second thought.

Augustus, while of course facing a different situation than his adoptive father, found a way to mollify the Senate to his rule. He still ruled with absolute power, backed by his control of the legions, but he masked this power behind titles and offices 'granted' to him by the Senate.

In short, my reading of why Caesar was assassinated was that near the end he went to far in accepting the honors and accolades heaped upon him, causing the reactionary forces in the upper class to fear for their treasured place in society. They feared that a further success in the East would give Caesar enough public support to declare himself King, and so destroy the Republic. Ironically, the assassination of Caesar did not restore the Republic, but led instead to its complete disintegration under first the Triumvirate and finally the Principate established by Augustus.