Fan servicing in Part 2 ruined the series.
fillers, lame animations, multiple projects at the same time. There wasn't any focus anymore. It seems like Kishi escalated it into DBZ-esque but never quite know how to end it while still sticking to the theme.
I mean he definitely knows how to end a conflict if its just writing fights. the most powerful/the most number wins the match but since he tries sticking to Naruto turning something that's gone bad back to being good required a lot of nerfing.
Also, the gaiden was fan service. he had an original plan but ended up with a fan service. WHY KISHi WhY? what was the whole point of the whole "NOBODY KNOWS WHO YOUR REAL MOM IS SARADA EXCEPT FOR KARIN! and I mean nobody. not even sasuke or sakura. NOBODY But KARIN" like really kishi?