The author is Shiriagari Kotobuki しりあがり寿, and the title is YajiKita in DEEP (弥次喜多in DEEP). It was serialized from 1997 to 2002; I read it in a 2005 book edition. It won prizes. I don't think it's been translated.
For the first half, I thought it was very amusing, even charming. For the second half, I alternated between feeling it was brilliant and finding it maddening. I think I ended on brilliant.
I think it can be mostly summed up by the convenient word hetauma. Google it. Good-bad, (un)skilled, pick your own rendering. The art style fits the label perfectly: on the surface it's artless, amateurish, school-desk graffiti level, but after you've read a couple of pages you realize nothing's accidental, nothing's drawn the way it is because of lack of control. And sure enough by the time you've reached the end you've encountered panels and passages of beautiful near-photo realism, nuanced effects of tone and line and shading, skilled pastiches of other artists' styles, and all manner of effective variations on the author's basic style. So it's obvious that the bad is an aesthetic choice, an embrace of amateurishness that opens the door to all kinds of experimentation. It unhooks the art from realism, so that anything's possible - including occasional realism.
Usually hetauma is used to describe the art style, but I would apply it to every dimension, every level, of this work. F'rexample, the adaptational aspect of it. As the title suggests, it's a riff on the old chestnut Shank's Mare, with two Edoites, Yaji and Kita, tramping down the old Tōkaidō to visit Ise. But it lowers your expectations immediately by having Our Heroes ignore a warning and take a right turn onto the new still-under-construction Super Dream Tōkaidō: we're given to expect that nothing is going to be like the original. And indeed there are precious few correspondences with the original, but it's not like the author is just using Kita and Yaji as an excuse for dreamlike happenings. He sticks closer to the frame than you might expect. He never totally abandons the early 19th-century setting, for example (despite all kinds of sly anachronism). And most of the surrealism is grounded in Edo-era fantasies, or at least jidaigeki renderings of them. The village full of religious fanatics at the end, for example, is clearly informed by an awareness of medieval ikkō-ikki. Indeed, the mystical symbolic significance Ise takes on from about halfway through the story is a kind of Godot-like existentialism that doesn't have to be, but really is, grounded in the source material.
Halfway through. Yes, it changes around then. For the first half it's (like the original) highly episodic. The moods of the various episodes range from nonsensically comic to quite horrific, and so the author has already succeeded in transcending the gag-a-page promise he seemed to be making at the beginning. But in the second half he goes somewhere completely different. The episodes all connect, and we start to get secondary characters, and then Kita and Yaji are transformed into a cross between Hindu myth-monsters and tokusatsu kaijū, and then they battle for a hundred pages straight, and then they drop out of the story entirely... It gets weird, dark, and super-violent, and the early episodes' flirtation with myth and religion reveals an obsession with the mechanics of messianic cults. And then we learn that maybe, just maybe, the whole second half was a dream, and/or an allegory of a boy's fears on entering puberty.
There's a whole documentary on it here, which I may someday have the patience to watch.