These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
A few versions/ports of the series also use a different sound effect for screeching tires, a high-pitched squeal that sounds more like a cat in grievous harm instead of rubber spinning on pavement. Especially noticeable in Initial D Special Stage, a port of Version 3, as many players would use a normal controller rather than the steering wheel of the arcade version, meaning they would have to correct their steering angle multiple times throughout a turn due to a smaller and more sensitive control radius. This led to the same ear-splitting squeal playing, stopping, playing, stopping, and so on continuously every time a player would go around a corner.
Scrappy Level: Happogahara in ver. 1 through 3 (and 5), Irohazaka and Myogi in Initial D 4. The latter, by the way, is supposed to be a beginner-level course, but it becomes scrappy when you combine it with a...
Scrappy Mechanic: In Initial D 4, corners have arbitrary speed limits that, if exceeded, will either lock your car's steering (in version 1.2) or cause you to spin out of control (in version 1.5 as well as Initial D 5).
Version 6 AA averts this, generally being more warmly received than 4 and 5, with Ver. 7 AAX being mostly the same game as Ver. 6 with added content.
That One Boss: Takumi when he's in the Trueno, his father Bunta in all of his appearances, and Ryousuke. There's even a mode in IDAS ver. 2 and 3 called "The Bunta Challenge" where you battle a version of Bunta who improves with subsequent races. It's the only mode where you can lose points if you lose.
They Changed It, Now It Sucks: Initial D 4 employs a completely different physics engine from its predecessors. Fans complained. Then the "version 1.5" update was released and changed some issues with the original version.