If it comes from the Shounen genre of anime then usually it drags on. I would say that in terms of Hunter x Hunter the first season is a drag. It does some interesting things, and introduces some of the weird eccentric characters. Beyond the first season you get a lot of well told albeit troupe-y story arcs. With the world they've built it's sort of cool, and not overdeveloped. The action is really great, and the characters even beyond the main character are really interesting. If you ever had a plan to watch Naruto, don't. Don't ever watch a show in these categories (only exception would be Hunter x Hunter). Reason being they are filled with literally hundreds of episodes that are only there so that the anime never catches the manga. This is why I'm always very reserved to recommend the very poorly designed genre that is shounen. It's literally just filled with mainstream garbage. Some of the early Naruto was very interesting, but somewhere along the line it lost what made it cool.
Naruto, Bleach, Fairy Tail, Sword Art Online, Attack on Titan, Inuyasha, and there are many out there. There is good shounen. My rule of thumb is usually the longer it is the worse it gets. To go along with the theme of samurai champloo, Rurouni Kenshin that's a good one too
There are a few aspects that make modern day shounen manga/anime very soap opera-y in my eyes. First is much like you said filler drags things out, and ultimately means nothing to the story. The rest of what you said is exactly right, with just a bit missing. They begin to warp the story into this unbelievably convoluted thing that really loses its footing all together. Naruto as an example. In the first few arcs we had a sense of meaning to every character. We knew Naruto was special, but it wasn't overwhelming. He was a person with a story we cared about. Other characters like Sasuke, Neji, Hinata, Sakura, etc. all had important stories even if they were still a bit troupe-y. The story wasn't centered around Naruto, it was centered around children essentially being brought up in the militarized state. Then after awhile it became very mythological and the story especially in the manga began to get out of hand. The characters lost their personal touch and the entire series slipped into the pit of melodrama as all soap opera's do. Once that happened the complexity of the setting, characters, and plots melted away. A lot of the story had no emotion besides the moments that they leverage our long-time attachment to a character by threatening their deaths or giving them a challenging opponent to face and become stronger. It was like we were being told mythology of Greece without the important thematic message embedded within it.