=w=....
Good question Korp.
One thing, another person's hate, is another person's interest. Anime is too broad, and to wide. Anime encompasses a lot of things,Light Novels, Manga, eroge, Visual novels, Doujins, etc. And many of them go into anime because people want to see it in action.
All what people hate in a certain anime may be it's plot or how the characters are acting or treated. Anime can be treated like any other fiction and any other thing, but the treatment of it is at a far deeper degree than a mere fanfiction or fantasy.
Here's a brief overview on it. READ ALL OF IT
There are a lot of genres in anime, Shounen Ai, Shoujo Ai, Bishounen, Bishoujo, Harem, Reverse Harem, Comedy, Ecchi, Mecha, Magical, Drama, Military, etc. And there are many Mangaka who may draw and write them ever so dearly, or Gensaku-sha who illustrates those who write the plot of a Manga. The most common is what Erebea said. It can also meld with secondary genres like Mecha or Comedy or Drama. Seinen is scarce and the least common is Josei. But Josei type works are slowly multiplying.
And again, Manga, whether the manga be a 4 panel or a complete chapter by chapter type, is not the only thing where Anime is limited too. Visual Novels and Eroges are also part of it, and it's where most of the fanservice come from. There are a lot of normal mangas around in Japan, (Which are sadly obscure to the normal average anime fan), like Kaichou wa Maid-sama, Ouran Host Club, 100% Strawberry, K-ON!, Nichijou, Ga-Rei, Suzumiya Haruhi no Yutsu, CardCaptor Sakura, Hunter X Hunter, Flame of Recca, Kure-nai, Bokurano, I could go on. None of them are harmful, but are fun to read, and they contain fanservice. I'll explain that in a bit.
Other animes such as Otome wa Boku ni Koi****eru, Oretachi Tsubasa wa Nai, Hoshizora e Kakaru Hashi, Higurashi, Happiness! were based on Adult Visual Novels, and hence the anime may or may not depict scenes from the said game. Higurashi though, was completely depicted in the Anime, since there's too little ecchi in it. The rest I said however, had some ecchi in the game, but the elements of it were removed from the anime. Or some of it.
SOME animes may come from unexpected places. One of them was Sengoku Otome--Pink paradox was based on a Pachinko Game. No it did not had the manga, nor anything JUST a pachinko game! Other animes like RIN ~Daughters of Mnemosyne~ are completely made first, followed by a light novel and manga adaptation. That goes with Occult Academy, Soranowoto and Senkō no Night Raid.
Now that's out of the way, here's my main point:
Everyone may hate the plot or the jokes or the slapstick because that's been a norm in a manga. The Mangaka or writer will make jokes or take jokes and will put in on the anime, they will take suggestions from the anime studio. The Light Novel or the Manga or the Video Game where the anime came from always will make more sense than the anime, yet most people are only after the anime for eye candy, to see it in action.
Why do animes get cancelled? Monetary issues and other factors like illness, business, ratings. A normal anime is shown around 11 to 13 episodes. If the DVD sales or if they make a lot of money out of it, then a second or third season won't be a problem, and it's not only the issue about money, it's about the fans expectations and reactions.
Fans tend to gather around social sites like Mixi, NicoNicoDouga and forums and blogs to discuss about the anime they like. Word can spread as fast as soon as you typed it. If they like it, then they will make it, but fan power and money issues are only why a second or third season will happen. The creator may refuse to create another anime season since making anime is VERY expensive. They earn very little than what they earn when they were drawing and writing the manga light novel. All the money the anime makes, goes to the anime studio. The anime studio makes the anime move, work and so on and such which.
All in all Anime is too complex. So did I stand off the beaten path? Maybe.
As to the plot of some animes. You may have seen a joke, but it will always appear. Cartoons in the US are more cliched than most animes, or the animes you see are "gimmick" animes to promote something, like Sengoku Otome which promoted the Pachinko game. Or Higurashi where it promoted more of the Games thanks to the anime which made more people know about it.
Fanservice is not ALL BAD. You heard me. I like it.
Fanservice may split into a few kinds, the Eye candy Fanservice, aka the ecchi you see, or the Shoutout fanservice where references are made numerous times throughout the episode either as part of the background or a line a character said. An example of type 1 is Sekirei, To Love Ru, Ikki tousen, Rosario + Vampire, Seikon no Qwaser etc. Type two would be Lucky Star, Sayonara Zetsubo Sensei, Seitokai no Ichizon, Seitokai Yakuindomo, etc. Most people I've shown type 2 NEVER get the references, which could attribute it to people not knowing what is going on, because Anime campaign happens while an Anime is currently airing, hence some jokes or references will never see the light of day.
Type 1 is what is hated the most in Fanservice.