If he had no intention to kill, it is manslaughter. If he had intention to kill, it's murder. This must be proven in court of law. Self defence does not include killing people unless the guilty have every intention to killing you. If the law was clouded with emotions/religion, all punishment will be done unjustly.

Unless the guy hit his head on a hard surface whilst falling, it's quite hard to beat someone to death with fists, which implies that the husband continued way past the point of the man being disabled/severely hurt/unconscious. 

My immediate suspicious is that it was driven by anger not self defense. Which is understandable but thankfully not condoned by law. Haven't read the full article but it sounds like the only account we have is theirs which could easily be falsified since the other guy is dead. One of the many reasons stuff like this can be an issues and why things need to go through the justice system.

No, it's not hard to judge. When he's outside in the hallway, it's pretty easy to see that he's unable to hurt anyone, so it's absolutely excessive force.

Also, if you actually beat someone to death by inducing severe trauma to both head and body, you can't just have done that by accident while trying to knock him out or subdue him. You have to have been aggressively attacking him. I don't feel sorry for the husband, he should get charged. Simple as that. I don't care if he did it in a fit of rage because his wife had called and asked for help. He murdered the guy and used much much more force than neccesary to protect his wife from the situation.

A lot of people dies from just a single punch. He may have beat him for half and hour or he may have landed a strong punch, hard to know for sure.

Even then, even he is not actively attacking someone, you never know if he is going to pull up a knife or something, I wouldn't stop until he is completely harmless as well.

Until it goes to court we won't know for sure if he was just standing in the hall. This alone makes it hard to form an opinion.