If you don't mind, I'm going to reverse your reversal and recommend some things mentioned in this thread.
Naruto and
Bleach.
One Piece didn't appeal to me, so I didn't watch past the first couple arcs, but it's in the same boat. These are good shows, good,
surprisingly smart shows with a lot of thought put into them. Er, well, except for Bleach. Kubo never had any clue what he was doing with that mess. Also, they're delicious snack food. You can easily gobble down ten or more episodes in a day if you have the time. Lastly, watching one of these keeps you humble, and prevents you from becoming an asshole who tells people they're dumb for watching shounen.
Attack on Titan. AoT rolled over the anime fandom like a wave. Very much like a wave, in fact. You could think of anime fans as a rock in the middle of the ocean and the rest of the Internet as a beach: the wave rolled right over us without stopping and then broke on the beach in a big, beautiful rush. Attack on Titan is fresh and fun and exciting and gritty and flashy and awesome...and it went over the heads (or perhaps under the feet) of monocle-adjusting otaku.
Neon Genesis Evangelion. Flawed? Sure. After watching Evangelion 1.0 for a second time, I can say that Hideaki Anno is a piss-poor editor. "Huh?" you say. Yeah. That movies cuts were
awful. Other than that, though, I don't know if there's any anime which can equal Eva's cathartic power. I'll be quiet now. You can stay and whine about how whiny Shinji is.
Lastly,
Fate/stay night. Not because it's good, I haven't actually seen it and have no doubt it's quite bad. But there is no way,
no way in any possible universe, that the anime could possibly be as bad as the visual novel on which it's based. The VN outclasses in terribleness everything else I am about to mention.
Fate/Zero is great, by the way.
Moving on to the suck!
Here's one people haven't mentioned:
Wolf's Rain. Yeah, Studio Bones seems to have a gift for adapting manga (they were responsible for a show you might have heard of: it rhymes with Null Petal Malcolm-ist) but their in-house productions seem to pretty much universally be clusterfucks, and - in my opinion - Wolf's Rain is the most fucked of all of them. Believe it or not, I'm
not going to complain about the recap episodes - in fact, I think those episodes
improve the show. For those who don't know, there are four recap episodes in the latter third of the show; I believe there was an epidemic of some kind at the time, and so those episodes simply couldn't be made. No real harm done, though, because the last four episodes of the series simply went onto disk without ever being aired. Except those last four episodes turn a tolerable 22-episode show with an odd and vague but surprisingly satisfactory ending into a confusing, ridiculous, almost amusing 26-episode failure of a resolution.
Honorable Mention goes to
RahXephon, which only escapes because it's by the same studio and has basically the same problems. It does, however, earn a silver medal in the category of Worst Opening Song.
Bruce said:
Elfen Lied. Its worst flaw isn't the nudity, the pointless cruelty, the violence or any of that.
It is that it is boring. It is one of the most boring pieces of crap I have ever watched, with stale, unrealistic characters, a plot trying to be so "adult" it raps itself right around to being juvenile again, and really nothing to redeem it.
Uh, what this guy said. I have nothing to add.
Another one nobody's mentioned:
Eden of the East. I'm honestly not totally sure what's so bad about it. It's bland, but lots of things are bland. But when I was ranking the anime I'd seen a few months back, I could think of almost nothing I liked less than it.
Witchblade. Hoo, yeah, so my problems with this one are the same as my problems with most ecchi anime, Witchblade just sucks at it the most. It has two basic problems: 1) too much fanservice, and 2) not enough fanservice. Yeah, this seems to be a thing with a lot of ecchi: dividing their attention to between story and titillation. Which is stupid, because let's be honest here, there's only one reason you're watching this show. It's like watching a porno in which the pool guy arrives, fixes the pool, they chat for a while, have coffee, have dinner, and then in the evening go upstairs and have sex. Except without the sex. And less interesting.
C: The Money of Soul and Possibility Control had a pretty great first episode. It's not as bad as anything above, but this is still a mediocre series with a cool premise but some infuriating idiosyncrasies. Like when the main character is in a battle and has all but lost after one attack, without his enemy expending any effort at all. Cut to after the battle, with the main character victorious with no real explanation. The worst part by far, though, is the ending. A plot-thing is about to occur which will erase Japan from existence. This is a known phenomenon which has happened in the past. The villain is attempting to save Japan. His plan, while it does require significant sacrifice, has no collateral damage. The main character opposes him. He has no alternative. In other words, if the main character succeeds, all 100 million+ people in Japan will die. The show has stated this. The main character succeeds. Japan is not destroyed, and in fact all the damage which has previously done is undone. HAPPY END.
Star Driver. If there is one show in this post you shouldn't see, it's this one. Do not watch Star Driver. I repeat, DO NOT WATCH STAR DRIVER. Star Driver is fun, exciting, and gorgeous, but it's also brilliant as hell and you won't get it. If you didn't like Revolutionary Girl Utena, don't watch this show. If you
did like Utena, don't watch this show, because Star Driver is twice as good. Seriously, STAY AWAY from the genius that is Star Driver.
What? You just said I had to Not Recommend an anime. You didn't say it had to be bad.