I loved it too!! it’s still a heartwarming show, amusing, and I love all the colourful, fun rivals and Iris is a very cute and funny main girl. TR’s various missions, like Operation Tempest and the Meloetta arc were really nice and cool.

why it’s hated: (aside from silly you-should-not-be-watching-the-cute-colourful-kid’s-show-literally-about-embracing-childhood-if-you’re-preoccupied-with-proving-how-much-of-an-An-Adult-you-are-like-jaded-Trip) the writers had plans they set up from the first season of bw! which they couldn’t carry out due to a mixture of real world natural disasters and tragedies (earthquake, Fukushima Daiichi nuclear disaster —> metaphor for nuclear power weaponized in the wrong hands in the whole meteonite plotline PLUS earthquake-like imagery and destruction of a city it’s still partly damaged/being repaired in later episodes… meant the first major Team Rocket plan and first appearance of Team Plasma got delayed indefinitely and banned/retconned out…

episodes got scrambled around… show lulled a bit while writers later repurposed animation and concepts from the banned two-parter for later TR plans and villain plots…

second season’s original plans, like which was the final gym or any use of the original incarnation of Team Plasma had to be put aside, to advertise a two-years-later sequel game no one expected instead of the usual third version aaaaaand lastly.

The league and the main rival being defeated in the preliminaries and folks not caring much for Cameron who has meant to be endearing and funny dumb hero protaognist-like traits but also came up with semi-Legendaries like Lucario and fully evolved Pokemon that made folks not enjoy the league very much. sliding back.
there were many tournaments before the league in this series, which made it very fun, but the lackluster league at the end put a sour taste in people’s mouths and after the pretty solid Episode N storyline, the Orange Islands-esque assorted fillers most clearly targeting the youngest audience put off people even more.

TL;DR climax of first major villain team plot got axed due to real world tragedies, scrambled order of episodes, advertising the games back then took full precedent over any story the writers wanted to tell so they were forced to change plans, and a bunch of filler at the end.

also, people hate Iris for playfully teasing her friends and having a catchphrase, not knowing the previous main girls had them too in the original (only Iris and Dawn’s catchphrases were dubbed in their run, Misty’s “tomboyish mermaid” and “world class beauty” intros only recently got dubbed, and Haruka/May in the original ended nearly every sentence in a way that made her sound unsure “-kamo” like saying “maybe” all the time…)