First of all, I think the sex scenes turned some people off into giving lower ratings than it deserves. This resembles Welcome to the NHK in that it's a story of flawed protagonists. Imo, the first half is entertaining, but the second half is coherent. The first half suffers from forced plot driving with awkward conflicts and dialogues that seem ridiculous at first. But honestly, that was a huge part of the entertainment in reading it that kept me going.
The farther along you get into the 2nd half, the pieces add together that really humanize the characters and reflect the current social problems of Japan. The events then became less ludicrous (unfortunately less entertaining, but the balance needed to be there I guess).
Overall, the story handles humor surprisingly well. My favorite part of the story is consistency. People get way too narrow-minded in "character development" into thinking that characters must change to be compelling. This manga is a great example that shows that "character consistency," or the understanding of someone by seeing how consistently he/she sticks to the guiding principles in tough situations, is a powerful way to humanize fiction as well. This can seem foolish, goofy, powerful, etc. But it was hardly ever boring.
I personally liked the art style despite its age but I can understand if others don't.
In conclusion, not a revolutionary character study, but Arigatou is a mediocre premise executed very well.
