What impression of Julius Caesar’s character did you get in Act I?
The answer to this question depends upon whom you are trusting to relay the "correct" information about his character.
In the first scene, Marullus says that Caesar should neither be cheered nor celebrated, since his victory for Rome has come at the expense of Rome's other heroic leader, Pompey. He chides the Commoners:
And do you now put on your best attire?
And do you now cull out a holiday?
And do you now strew flowers in his way
That comes in triumph over Pompey's blood?
In Scene Two, which opens with Caesar, Antony and Calpurnia, Antony says, "When Caesar says 'do this,' it is perform'd," suggesting the power and respect that Caesar has amongst his fellows and people. And, in this same scene, once Brutus and Cassius are alone onstage, Brutus says that he fears "the people/Choose Caesar for their king," and in the next breath assures Cassius that he "loves" Caesar "well."
However, it is Cassius, a great talker in this play, who has the most to say about Caesar that might form an audience member's opinion of Caesar's character. He describes how he saved Caesar's life when he nearly drowned, bemoaning how "this man/Is now become a god." He goes on to show how weak and unworthy of praise he considers Caesar:
. . .Ye gods it doth amaze me
A man of such a feeble temper should
So get the start of the majestic world
And bear the palm alone. . . .
Why, man, he doth bestride the narrow world
Like a Colossus,and we petty men
Walk under his huge legs and peep about
To find ourselves dishonorable graves.
If we are to let Cassius sway our opinion of Caesar, we will conclude that Caesar is all pomp, circumstance, and fine platitudes on the outside, but is as weak and fearful as a little girl on the inside.
But should we, in Act One, believe what Cassius says? Caesar enters just after this scene and makes a particular point to single out Cassius for his "lean and hungry" look, as a man to be feared, if, in fact, Casear was a man who felt fear. Caesar says:
I rather tell thee what is to be fear'd
Than what I fear: for always I am Caesar.
These seem to be the words of a very self-important man, but for my money, there are so many opinions and points of view when it comes to Caesar in Act I, that it is not very easy to arrive at one particular impression of his character. So, depending on whose word you trust, Ceasar is either a well-loved, celebrated leader about to be crowned, or he is a self-important fake who has no right to assume the lion's share of Roman power.