@KaitouRobin
2. That's clearly fan service. I personnally don't care about it. Not needed for me, but no problem either. Guess if I was still a teenager, I would enjoy that.
The author seems to like to include girl and boy interactions, Initial D was actually more crude about it. But it was also interesting, seriously introducing Enjo kōsai, something you don't see that much in mangas (it's generally either comical or excessive smut, but rarely serious).
He's always mixing car racing and people's story. That's actually a good part about him to me.
3. There wasn't commentary like that in Initial D manga either. It seems like he's doing a lot of filler yeah.
4. About that, and what I said before, I just think that he's a kinda average mangaka actually. His art is not very good, and he doesn't seem to be very good with writing stories as well.
He became a legend because he's doing great stuff talking about cars, but that may be all.
However, Initial D serious side I mentionned earlier was interesting. Including good slices of life really can improve a manga.