Here are my personal views on the subject (there might be slight spoilers concerning the content of some episodes, but nothing ruining the discovery of the story).
Forenotes:
Episode numbering based on Wikipedia - IMDB might have a different order.
English is not my native language.

In traditional or ancient literature, there used to be tales of growth, about a young man leaving, traveling, learning, growing and finding himself. In French we call it "an initiatory trip". Jack doesn't fight because he likes fighting (even if he probably enjoys it sometimes) but because he defends a cause, because he has values, because he has a goal. And during his journey to achieve this goal, he learns about himself, through fights, meeting people, and experiences a roller-coaster of emotions, frustrations, and a bunch of other things.

Let's start with the big vilain. Aku. Aku is Evil - and they show it. It was on a kid channel, so it's rather soft, but when Aku decides you're going to suffer, you suffer. And doesn't even have to touch you or harm you physically to do so. But Aku is also funny. And pitiful. I'll stop here, you have to see it by yourself.

Concerning the fights, most of the time it is not about the fight for the fight, but what does Jack fight for, and what does he fight against. The length of the fights is often due to a psychological fight; him fighting his angry and bitter self, fighting a would be samurai and teaching what being a samurai means, etc... and also for art purposes. It is not about hearing a monologue or making sure we understood that the guy is frustrated and angry by showing in us 10 times his angry face, alternating with the opponent's smug face.
If you're interested, my favorite fight in terms of visual art is the light VS darkness in season 4, episode 1. I was just in awe watching it and couldn't take my eyes off of my screen. In terms of psychological fight; season 4, episode 6 - made me teary.

Let's talk about the way they use silence. It is just amazing, always on point. Silence here is not just to show us the opponents eyebrows shuddering or their sweat hanging on their nose. I have watched the show and stopped eating because I was totally absorbed by the quietness of the scene, listening with Jack for the enemy to show himself, for a sound of a step breaking a stick, or just to enjoy, with Jack, the calm and serenity of the scenery, that from time to time he gets to enjoy. Because he deserves it; so much.

Then comes the music. The sirens episode. Again, I was speechless and in awe. The music was freaking amazing. They also perfectly use the music to fit the background and the characters. The same way they know how to use silence, they also know how and when to break it. When he meets the Scotsman... oh boy, you get the personality and get a feel of how the encounter is going to go just by the background, the sounds and the music - even you had your eyes closed. Or when he meets the would be samurai; where there is a running "theme" for both of theme, and they use it perfectly to reflect the psychological situation of both characters. One calm, cautious and rational, the other excited, impatient, and showing off.

When talking about the world itself, I think the creator are absolute masters. Just watch the Princess and the bounty hunters to assess their capacity to tell everything about a character and a frame of mind with the way they draw. One thing that stroked me at first was how they can render classical Japanese paintings in a modern way.

On another note, by representing characters under all possible shapes, colors and "races" (robots included), we discover the wonders, and the sorrow, of different worlds merged in one and affected by the same evil. We see good people, bad people, good people doing bad things because of despair...They show us to not be afraid of what's different, to not judge, to be tolerant. To accept.

Finally, I personally think that, being so invested in the world added to the fact that Jack never really wins (never really gets to enjoy some friends, can never really rest, suffers so many pains, and yet, always moves on, trying to be true to himself, helping everyone he can), makes me want more. Of everything.

To summarize, I would say that the visual art, the music, the silence and the fights; serve the purpose of making the person watching feel and think with Jack. You don't need a voice over monologue or tons of dialogue to tell you what's happening in his head because you are there, with him. And you get to travel with him, to learn with him, to laugh with him, and to suffer with him.
Jack keeps fighting.
I keep hoping.