What are your feelings about Cassius by the end of act one?
By the end of Act 1 of Shakespeare's Julius Caesar, the reader has received both direct and indirect characterization of Cassius.
Caesar doesn't like or trust Cassius: he says he has a "lean and hungry look," and that he "thinks too much." Caesar says men like Cassius are "dangerous." He says Cassius sees the motives behind men's actions, and will never be happy so long as he is in the presence of someone better than him.
Antony says Cassius is harmless, and is a "noble Roman."
And Brutus trusts him and thinks he is exactly as he appears. Brutus responds to Cassius with:
That you do love me, I am nothing jealous [I have no doubt].
Brutus does not immediately consent to side with Cassius against Caesar, but not because he doesn't trust Cassius, but only because he isn't yet convinced that it is the best thing for Rome.
The above are examples of direct characterization of Cassius.
Indirectly, what the reader understands from Act 1 is, at least in part, determined by the reader's ability as a reader. One may see a noble Roman trying to talk Brutus into doing what's best for Rome, or one may see a manipulative flatterer who's trying to get a more famous Roman to join with him in an illegal conspiracy.
What you see is up to you. I can't answer that part for you.