General

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Sword Art Online Season 1 was filled with fillers. It had one good episode, then went into a bunch of irrelevant side quests and stories. The whole SAO series was horribly adapted and was a huge waste. The fight scenes, while great for its time, were very few. There was very little character development outside of Asuna and Kirto's romantic relationship, which also felt forced at best. All the characters serve their own different type of cliche, like they're doing it on purpose. I think people need to rewatch SAO if they think it was anything better than average. Premise was good, animation was nice, hype was real, but execution was just awful.

Amnesia and Little Busters - I couldn't get through the first episode for neither, just that damn boring

Blood-C. The only thing that got me through was the gore, that I loved, but the rest... blank af, especially the first 8 or so episodes were the same: wake up, got to school, sing the same stupid song each day on the road, nothing happens at school, go back, useless talking, then fight in the night. Like what the hell, is it that hard to do something interesting?

SAO's first arc was damn great, that's the only one I loved and had amazing potential, then it simply when down the drain. SAO II first arc was.. at most decent

Alien Nine was pretty bad.

One piece

@bleute: I heard X and Y was really good.

I don't know how I ever watched Pokemon as much as I did when I was a kid. I guess the first few seasons were alright, but after a while it was more redundant than credit card insurance.

I don't really think I could name one I could say is the worst, there are a lot that are really, really bad in their own ways.

That said, basically any of the "cute girls doing cute things" are what are the worst imo.

Aku no Hana. They tried too hard to be different and ended up being terrible.

@bluemistar: how about "heads will roll" or "off with his head"?

heres an anime review i love https://www.youtube.com/watch?v=0W32e1rKCXw

Bleach is the only anime I hate and its popularity annoys me. The reason why I hate it is because it takes the bad out of Dragon Ball Z and leaves out the good.
The fights are the same where the only thing that matters is the transformations. Its gets really boring, really quickly. Much like DBZ, the main character gets most the power boost (in Super it gets worse). Maybe I missed things and the other characters got cool power ups, but its pretty unbalanced.
The good that comes from DBZ (besides nostalgia) is the was it tells a jokes with a straight face (for example, Cell v. Vegeta). In Bleach, the story can be repetitive and people who watch Bleach knows what I mean.
I'll probably remember more reasons later on.

I really didn't like SAO.

It started off okay...but as things progressed it became more and more corny, silly and just nonsensical. Part of the thing is that in order to enjoy a story, especially one like SAO, you need to be able to suspend your disbelief and allow yourself to become immersed. I just couldn't. I don't mean to sound cynical or like I'm taking this too seriously and trying to act smart...but I just felt like they were asking me to suspend my disbelief and believe the plot mechanisms with far too little depth and nuance behind them in order to do that. I couldn't remain immersed in the story...and the longer that went on the dumber it all felt.

Again...I don't mean fans of it are dumb. More than anything this comes down to my personal preference and tendency to just dislike the Sci Fi genre in general...as opposed to anything having to do with the specific plot in SAO.

I only enjoyed the first season of SAO. I just couldn't bring myself to finish SAO II.

School Days - I just don't know what to say about it.

SAO just got worse and worse. I dropped SAO II on episode 3, couldn't stand it.

Hunter x Hunter: The Last Mission (Movie) - a total betrayal to everything the franchise stands for.

Fullmetal Alchemist: The Sacred Star of Milos (Movie) - almost nothing to do with the show, the new characters suck.

ChäoS;HEAd - very poor adaptation which didn't hold up in any way, shape or form. The OP was pretty good though, same singer as Steins;Gate's.

Soul Eater NOT! - huge disappointment, very dull and boring.

Young Black Jack - huge betrayal to me as a Black Jack fan.

Chrono Crusade and We Without Wings. Fought to make to to five episodes before I tossed both aside.

Sonic X is just amazingly terrible. Then again I watched the 4Kids dub before watching the original Japanese dub, but either version is just plain bleh.

Higurashi Outbreak - This movie makes me cry (HAH!), since the lovely reception and response Kira had they tried going back to the gore fest the original 2 seasons had. Only problem, that wasn't the point of the show, and I remember a lot of people were like "Yay! Rena is crazy and blah blah blah". The overall standards a lot of them had infuriated me. Granted it's subjective and all that's fine, but we all get angry over the minimalist things!

Body Transfer... Yes, it's one for the perverts! Don't give me that look! I was a really weird kid back then!! *Ahem* Anyways the reason I hate this is PURELY for the ending. It doesn't explain what happened to the other characters! Basically the one guy and his neighbor girl get together back into the normal world and have some wild tango on the roof of their school, but COMPLETELY forgetting about the rest of the classmates entirely!

Oddly the Visual Novel the thing was based off of actually had an actual conclusion from what I heard. Either way I got so angry from the animated version I actually wrote an episode 3 & 4 just to actually put a period on the whole darn thing!

SoulTaker - Tatsunoko's first attempt at making an adult show!... and it kinda sucked! I mean it was trying to be too edgy I feel. Then again it spun off and made Nurse Witch Komugi-chan & Z which were both lighthearted silliness. The latter I actually enjoyed, and I became so stupid from it I actually went and bought ALL the related albums for the show! All 20 (or 21?) of them! *Shakes head* Confound it past me.

Ghost stories. But the dubbed is great.

I remember watching one called Chrono crusade or something like that, man what a crappy anime that was

@renexz: This is a solid choice. I agree. Blood-C was a disaster.

Blood-C. OMG this anime is terrible. The story is all predictable, and the character are cliche af and idk I don't like the "monsters killing people" genre, I'm more like "people killing people with tons of gore" genre, so yea, pretty sh-t.

golden dream or something
this are the worst things ever created IMO

Mars of Destruction.

Maple Leaf Saga.

definitely not boku no pico

I'd say Fate/Stay Night. There's supposed to be this epic tournament going on between legendary heroes like King Arthur and such, but in the 12 and a half episodes I was able to force myself to watch, I saw maybe 2 fight scenes, and they weren't even very good. The main character is horribly sexist and horribly stupid, forcing the magical warrior he summoned (who is there for the express purpose of fighting this battle) to stay at home because she's a woman. Instead he fights and gets his ass kicked consistently. Character motivations are all screwy, there's no reason for Rin to want to team up with him, and the magic in the show seems to make up rules along the way. It's really bad.
It's baffling that this piece of garbage was made by the same studio that made Higurashi no Naku Koro Ni, my favorite anime of all time.
Honestly the magical girl-style spinoff Fate/Kaleid is considerably better. People often look back on Fate/Stay Night with rose-tinted glasses, since it was generally among their first experiences with anime. But yeah, I'd say it's the worst anime I've ever seen.

SAO is fine, people hate on it unreasonably.

There's a few contenders for me. One I can't remember the name of (I watched it one time, deleted it and didn't add it to my MAL sadly).

Mars of Destruction is at or near the top though. A 20 minute episode of... what? I don't even know. There's guns and lasers and the slowest. Possible. Movement. Ever. Like there was a laser gun fired (or whatever it was), there was a 5 second delay, then someone gets hit. Except they dodged it. Or something. I don't even know. It's just awful production. Awful (short) story. Music that doesn't fit at all.

The other would be Baccano. It's super highly rated for reasons beyond me. Terrible character naming. Jacuzzi? Nice? ... yep. There's a gigantic cast of characters, which is usually not a problem. Except they're super flat and get ZERO character development, making their actions unbelievably predictable. Then there's the nonsensical time jumping that is bewildering. Oh, terrible logic too. "Hi, what's your name?" "Oh my name is xyz" (...wait, why did I just give them my real name? There must be an immortal nearby!" .... really? REALLY? That is stupid as bleepity bleep. Oh, and the hand sucking. Ugh. So stupid. I hate this series. I was only able to get through it because I was drunk off my rocker.