Most of those who hate this anime are those who think that Yokai Watch is a copy of Pokemon (I do not believe that to be honest, they may have a similar fighting style, but the protagonists and other main characters are totally opposite to the Pokemon) or the other majority of those who hate Yokai Watch are those who do not know that it is an anime for children.
The plot may not be varied, it is the protagonist trying to deal with the problems he has in his life after connecting with the yokai / ghost world and learning more about the yokais, but it is like that since children's comedy animes do not usually have a very dramatic plot.
The characters are very funny and each one has a unique design, for example Jibanyan or Komasan, both are very cute physically and are very easy to love because of their personality, also the protagonist, who is annoyed for being normal when he really is not. .
Animation is the weakest point of anime as it is not bad, but sometimes I see some animation flaws.
And lastly, the music is very catchy haha.
Final opinion: Yokai Watch is a good anime, with good and bad points, it is not perfect, and it is hated for being childish or for being confused with other anime, but personally I like it a lot for the unique grace that anime and the cool characters