Why did the show become so vastly different after season 1?

I recently started watching the show and season 1 hooked me. It was phenomenal. Every episode was exciting and important and the general atmosphere was very unique with a theming I've never seen before. Then I watched season 2 which honestly was just very boring and bad. At least the atmosphere was kinda the same. And yesterday I finished season 3 and I just felt like I've been watching a different show. It was so goofy and childish and some aspects of the story were straight up stupid and unrealistic. Especially the Russian storyline with the Dustin crew. Felt like it was straight out of a kids movie.

What also bugged me in season 2 and season 3 is that every episode felt like a filler for the huge climax in the season finale. Season 1 wasn't like that. I enjoyed every single episode because every episode felt HUGE in terms of story developing.

Is there a reason for that? And without spoiling me, is season 4 even worth watching if I did not enjoy season 2 and season 3 too much?