I would go the other way and say I was impressed with the importance that Brutus carries about him. Even though we really aren't given much about Brutus, it is apparent that he is a man of great worth. Not only does Cassius spend the entire first act trying to convince him to join the conspiracy, but Casca also knows he's important enough to tell what happened at the Capitol that day. We are able to see Brutus as an extremely important asset without knowing exactly what it is that made him so important.
I suppose Cassius made the biggest impression on me, simply because he's such a smarmy jerk. He's like an oily, used-car salesman (nothing personal to any used-car salesmen out there!) that knows exactly what to say and who to say it to. A politician...that's what he is! Caesar describes him perfectly when he says he "has a lean and hungry look." (1.2)