Boy, we're gonna be here for a while, mostly because it's a long list. I will provide expalantions for all my choices, but they will be civil. Well, let's do this!
For the convenience of others in the poll, I'm going to link the TZ Wiki's list of action shows. Y7 filler shows do not count because they were just that, filler. Although they were probably an ill omen of things to come.
#10.
Blood+ A sequel to a one-shot movie which was much longer but also much more boring than said movie. It also seemed to be chock full of that 75% dialog, 25% actual action formula ASA uses for most of its shows. Dull and boring.
#9.
Mobile Suit Gundam: Char's Counterattack. Settle down! I love Gundam! Char's Counterattack is an awesome ending to one of the greatest anime sagas of all time. But it's the ending to a show that we never saw the entirety of. We saw half the beginning (MSG) and none of the middle (Z and ZZ). So airing the end seemed kinda strange. I love the film, but any Gundam newbie watching it will feel entirely lost as knowledge of the previous events is a MUST to understand what the heck is going on and why you should care about these people.
#8.
Reign: The Obsession of Alexander. For whatever reason, Peter Chung is still getting work from his Aeon Flux days. What was a sprawling and actually well thought out epic was doomed by one simple glaring character design.
NONE OF THE MEN WORE PANTS.
That alone completely killed the interest in the series. The character designs and plain unlikeable characters (Alexander was a noted jerk in real life who literally bawled and cried to keep his troops pressing into India) made sure this was one of the worst examples of what ASA had to offer. It's a shame because if the character designs were done by...anyone else, the show might have been redeemable.
#7.
Android Kikaider- A TV-PG show that's actually an update of an old tokusatsu show from the 70's with a villian that George Lucas cited as inspiration for Darth Vader? Sounds decent enough, except for three major problems.
1. The animation was practically non-existent.
2. The concluding series OVA was cut to shreds including the epilogue.
3. Unless you live in Hawaii, odds are you have no connection to Kikaider as a kid.
So yeah, a PG nostalgia revival that was disconnected from said nostalgia and not good enough to last on its own merits. Making it #7 on the list.
#6.
Paranoia Agent- Utter boredom and pretentiousness crammed into 22 minutes of Saturday night TV. A complete ratings bomb from all sides. The more I saw it, the more I had this weird (but unproven) feeling that AS wanted something like Gantz, couldn't air it due to the violence and sex, and went with this show instead, the complete opposite. This show did terrible, and the worst part was it became the standard bearer for what ASA wanted their shows to resemble.
#5.
Astro Boy- A museum relic is the best way to describe the 60's Astro Boy. Something to be admired, appreciated, but decidedly NOT practical for the modern audience. So when Mike Lazzo chose to air it because he personally liked the series, head banging ensued. It's not an adult show, and the retro factor holds up for all of one episode before someone wants a new show.
#4.
Case Closed. Well, I'm running out of positive things to say the deeper we go into this list. Case Closed is a kids show. There is no getting around it. Airing it on Adult Swim makes about as much sense as airing Beserk on DisneyXD. It just doesn't fit. And not to mention, it's incredibly formulaic. Someone dies, Conan drugs detective, reveals the killer. It's not an adult show, and as far as mystery shows go, it's not sosphisticated enough to grab people outside of the target audience. If killing people was kosher for kids TV, it would make a wonderful DisneyXD or Nick show.
OK, that was positive. I still think Case Closed above all was a victim of mismarketing rather than being a genuienly bad show. But I'm not the right age to enjoy it.
#3.
Witch Hunter Robin- Unlikeable characters, terrible designs, and a boring formulaic plot combine into a horrible meandering experience for all. This show was apparently supposed to get a live action adaptation on Sci-Fi, then the show aired and everyone realized it would be a really bad idea.
#2.
Eureka 7- What can you say about Eureka 7? The romance angle is immature and feels like it was made for a 4 year old girl. All the character designs are ugly save the skysurfing robots. The characters are jerks. The main hook of the story does the exact opposite and drives you away. So you create a really, really bad romance that just happens to have romance in it, proving we were a long way from the days of Dangaioh where the pilots were competent. Godannar did it in reverse, but well, Godannar was better on all angles, while Eureka 7 crashed and burned one week in, making it #2 on the list.
And the #1 worst anime on Adult Swim is...
Moribito- Guardian of the Spirit.
This is it. THE worst. The absloute worst show they could have possibly gotten at a time when they NEEDED a hit. You need a show with nonstop action? Moribito makes Tom Goes to the Mayor look like Die Hard at points. You need a show with an involving plot? Moribito is about as engaging as a lecture on Kant. You need something with thrills and suspense? Moribito brings you snoozes and snores. It felt like, in essence, Adult Swim saying "you know what? This block is doomed. And we don't care. So we'll air this bomb and you'll ignore it just like everything else." So not only was the show bad on its own merits, it reflected a "WE DON'T CARE!" attitude from Adult Swim as a whole.
So there's my bottom 10. If you have any objections, feel free to PM me. I'm more than willing to listen to criticsm you may have.