Let's start with the strong/unpopular opinions so people can react how they want to react and not have to spend all that time reading a review.
A. Initial D's Manga is only truly great after the anime.
B. Initial D's Anime looks dated as !@#$, and is not as good as the manga because of that.
C. A number of characters have "DSL" entirely too often (early on). Worse in the anime, but exists in both.
D. The romance sub-ploits SHOULD HAVE BEEN REMOVED. They add absolutely nothing to the series and at best could have been limited to one race, but really shouldn't exist. And that includes every... single... one...
Honestly, do I have to review the manga? I've said what I really wanted to. Ok I'll do it anyways, or at least explain these points.
First off Initial D is about a Tofu delivery man who gets into the world of "Touge" racing, which is mountain course racing. Now let's get to the biggest, perhaps most important point about this entire series.
Physics don't exist in this world. Period. There's no universe where "drifting" is the fastest way to get down the mountain on every corner. There's no universe where a AE86 would be able to beat most cars it races against here. There's so much plot armor on Takumi Fujikawa that it's more of a question of "how" not "if" he'll win most races.
That being said I guess it's time for the big reveal. I LOVE THIS SERIES, but I do think there's important reasons why I love it.
First, The tv show was amazing when it first came out in the late 90s. It had CG models racing, an amazing Super Eurobeat sound track and just incredibly cool. But it's been over 20 years since then and... to be honest the anime has aged poorly, the cars look flat, the drawings are a bit weak, the animation is cheap by today's standard.
But I talk about the TV show because so much of my enjoyment of this series has revolved around the amazing Super Eurobeat soundtrack, if I wasn't listening to that while reading it, I probably couldn't enjoy it nearly as much. However the art of the cars in the manga is fantastic. The cars are extremely well detailed and while the first section of the books have the best story, the art by the final sections are brilliant.
The characters... I really feel like Ryosuke and Takumi look too similar after a while, a number of characters are forgettable because they have such generic designs and more... but that's not what you come to Initial D for... it's the racing, the cars, the battles, and that... that's where this anime shines.
In fact the only real problem I have with the second half of the books is that some chapters are just 8 pages of racing, and while it's a beautiful 8 pages... it's easy to just rip through these chapters like they're nothing...
There's a lot of story in the manga, and while Takumi's evolution does matter quite a bit, the relationship stuff (as mentioned before) is really the only bad part because there's so little point to it. I know there's a few things that happen related to the relationships, but... the relationships aren't really required to have those events happen.
Overall This is the series that made me fall in love with Racing, Touge, Driving, and Super Eurobeat and ultimately reading the entire series now just reminded me of all those epic amazing feelings. Maybe it's because it reminds me of when I was a kid, and this anime came out, but I don't know. I still think there's a lot of enjoyment to be had reading Initial D.
This series is WHY I turn on Super Eurobeat any time I'm playing a racing game... I know I know. That's the "Anime" But give it a shot when reading the manga too, you should understand.
And sorry, this is probably a rambling set of thoughts, but that's also kind of what I want my reviews to be. Hopefully it'll help you... or maybe it'll only help me finally stop thinking about this series every single day.