I don't want to be too picky, but Caesar was not an emperor (Rome wasn't an Empire, but rather a Republic while he was alive). For about a month before his assassination, he was the officially elected "dictator until death,"(which you could probably say is pretty close to being an emperor) and before that just a "dictator," which was a temporary role that held the highest authority in Rome's system of magistrates, but still not complete authority.
His successor, Augustus, is considered to be the first Emperor of Rome (Caesar did a lot of the groundwork that led to Rome being an empire, but it didn't all come together until after his death).
Caesar was able to do great things specifically because he was a dictator! Don't get me wrong- when we use the word dictator today, it means something very different from what the Romans meant when they used it. In the Roman Republic, a dictator was someone temporarily appointed in times of crisis to take over and "dictate" what was to be done in order to fix things. Caesar's dictatorship was an extended one (they usually could not last longer that 6 months) and was meant to bring an era of restoration to the republic.
In addition to deeds listed in the previous answer, Julius Caesar also accomplished the following:
- Gave rights of citizenship to the Italic tribes outside of Rome
- Showed mercy to his political enemies (which was not a great move for him because those guys ended up being the ones who killed him)
- Changed the Senate so that is was more representative of the people
- Was just in general a man of the people, working for rights and resources for the lower-class people of Rome rather than just the aristocrats