I think raagnorok said it all. First season is great because the scope of the story is focused on a handful of characters to whom we get attached. Second season is already a lot worse because of the sheer amount of groups we have to follow and sadly, most of the new characters are completly uninspired. I barely read season 3 because i already struggled to finish season 2, still since the quality of the story kept running downhill, there's no reason to assume it's going to get better. I simply cant get invested in characters i dont care about at all. The author failed to keep the quality up when the story went from a smaller scale to the huge scale it stands at now.
The universe in this manga is amazing. And the art has really improved since the first chapters. But the story has devolved into a sea of poorly written character, uninteresting stories and overused tropes.
It went from an 8/10 to a 4/10. Unfortunately, this kind of thing happens too often in shonens. The author are great at creating a universe, lovable characters and so and so on, but they simply fail to keep the story at a decent level when the scale of the world is getting bigger and bigger.
That's the difference between Berserk for instance, and ToG.