First and foremost: Akira Ishida plays the main character. And since we're in love with Akira Ishida, this is almost enough by itself, especially when you can see how talented he is by playing such an anti-hero after playing such characters as Hakkai, Athrun, etc... well, actually, he played those characters after Gokudo, but we heard them first, so...
Anyway, it's not really enough, to be honest, because there is a series where Ishida-san plays the main guy, and is adorable, and even sings (an adorable song about how awesome his character is), but we never really got into it. Of course, that was before we were in love with Ishida-san, so perhaps a better example would be Onegai Teacher. Soichiro Hoshi is the main character, and, despite the fact that Hoshi-san was our number one favorite voice actor at the time we watched it, I hated Kei.
So in my other entry, I talk about how we like serieses that show characters caring about each other, learning their lessons, and taking responsibility. This is exactly why we would probably hate Gokudo, except for one thing: the genie.
As soon as the genie started lecturing Gokudo about how people these days don't know how to make good wishes, we knew this was going to be an entertaining series. And then he turned Gokudo into a girl. You can't beat that. The second episode introduced Seigi, who, of course, is our favorite character. And from there, we had to keep watching.
The storytelling is done very well. We've seen many a series or movie where the idea was good, and the characters were kinda neat, but the storytelling just didn't work. In fact, I have a suspicion the creators of The Island think along the same lines sometimes, because I seem to remember seeing a movie with that same premise on MST3K.
Another thing that ought to be taken into consideration is the timing of when we saw the series. We discovered Gokudo at a time when our roommates had decided that, at our best, we didn't exist, and, at our worst, we were to be avoided like the plague. Many of the people we went to for support during this didn't have much more to say than, "Maybe you're not trying hard enough." We felt we were trying very very hard, so this had numerous adverse psychological effects on us. But there are two effects this had on us that probably would have existed whether we were really trying hard or not, and these are the two that would have helped us to like a series like Gokudo.
The first effect is that we were very insecure as to our own state of goodness vs. evilness. If we weren't trying hard enough, then it was probably because we're bad people. Seeing a series like Gokudo would show us that there are ways to be worse than we were being, and would have been a self-esteem boost.
The second effect is that it would have caused us to want to do evil things to the people we felt were causing us injustice. Watching Gokudo would have been a way to get that out of our systems without hurting anyone else.
Also, it's nice to see bad things happen to bad people. Gokudo usually has to suffer for being the way he is, and I admit that I like to see people get what's coming to them. That's why I was so amused in TideLine Blue when the main guy slammed his hand onto the submarine and it froze there. He does get some cool powers that he probably doesn't deserve, but the traits that got him those powers are ones that I tend to admire in people, or at least think that people should have.
Still, I think the most important thing about Gokudo that helps us to like it despite the characters' evilness is that there's no pretense. Gokudo is the scum of the earth, and he knows it. He just doesn't care. Also, all the people around him know it, and let him and everyone else know they know it. He's not set up to be any kind of a hero; he's the textbook definition of an anti-hero.
In contrast, we have in America serieses like Lizzie Maguire (if that's spelled wrong, we'll say that it's because I refuse to dignify the name with a proper spelling), where Lizzie is set up to be the heroine, but we can't see much difference between her and the antagonist. Granted, this could be that we haven't seen very many episodes. We could chalk it up to bad writing/story-telling, but you could say that Lizzie Macguire is a more realistic series. I happen to be more of an idealist, and think that we don't want to be encouraging people to be like this just because most of them are. Which again contradicts our love of Gokudo.
But back to the no-pretense thing. It kind of reminds me of the one scripture about not being lukewarm. Gokudo is definitely not lukewarm. It's the same reason we like Saiyuki. If anything, the pretense is that they're worse people than they are. None of this, "I am the good guy... but I'm gonna let this village suffer because it's too hard to save them." It's just the opposite--"We're no good guys. But I guess we might as well help you out while we're here."
Gokudo doesn't have the helping out thing so much. Or at all. But at least we know what to expect. In the immortal words of Captain Jack Sparrow: Me? I'm dishonest, and a dishonest man you can always trust to be dishonest. Honestly. It's the honest ones you want to watch out for, because you can never predict when they're going to do something incredibly... stupid.