Interrupting another candidate during a presidential debate is not a positive character attribute. It is emphatically not presidential. It is rude, and shows a petulance that is not conducive for a would-be president. A president needs to be able to listen to differing viewpoints, and not just shout down those that disagree with him or her.
A candidate should not have to rely on the quantity and volume of what they are saying to get their points across. They should have the eloquence and insight into the challenges of the job of president that they can get their point across persuasively in the time allocated to them. Both candidates deserve equal time to get their values across, and interrupting the other does not hold to this.
In the end, they were not debating one another but using the platform to speak to groups of people they have already secured (Trump) or are still grasping for (Clinton). Donald Trump was vintage Trump—unscripted, emotional, angry, and railing against establishment politicians, which Clinton epitomizes. But Clinton was vintage Clinton as well—super-prepared and perhaps overly scripted and cautious, but confident when under attack, with lines that were effective at times but also clearly canned.
Donald Trump set a record for interruptions during his debate with Hillary Clinton. He interrupted her a whopping 25 times during just the first 26 minutes of the debate. This reflects badly on his character: if he can't let other people finish their thoughts, then how will he ever be able to receive constructive criticism in a job that requires an individual to listen much more than they talk?