Throughout all of the series, the cars have been organised according to some common defining feature: 4WD class cars are obviously 4WD, FWD cars are obviously FWD, and so on.
DiRT 2 abolished this practice by instead seperating the cars into their respective event class (rally, rallycross, Raid T1 etc.). However, cars could be upgraded or downgraded into Rookie, Pro or All-Star classes.
DiRT 3 seperated the cars into their eras; such as '60s, '70s, '80s and so on.
DiRT Showdown utilises an upgrade system, meaning players take all cars (with the exception of the Gymkhana cars) from D class to A class.
DiRT Rally is similar to 3, with the rally cars separated according to their eras (Except for F2 Kit Cars and R4 Rally, Group B cars are separated into both AWD and RWD). The hillclimb cars and rallycross supercars are in their own catagory.
DiRT Rally 2.0 newer cars are fitted into similar categories as in the previous game, but older cars are now divided into H1, H2 (FWD), H2 (RWD) and H3 categories. These categories mostly follow the decades that the cars came from, but are aimed to be more balanced, with more powerful cars from '60s and '70s, like Alpine, 240Z and Stratos now competing against newer cars.
Contested Sequel: Many people who sank tons of hours on DiRT Rally see 4 as a step-down compared to its predecessor in terms of handling. The random stage generator has also caught some flak due to recycling stage sections. However, that doesn't mean the game doesn't have its fans, who appreciate the discipline variety, the gameplay, and the team management aspects.
Renault Alpine in DiRT Rally is an RWD car in the 1960s class that beats most 1970s cars in terms of handling as well as performance and driving Alpine is often mockingly described as "easy mode" by players for this reason. Indeed, it's not surprising that in DiRT Rally 2.0, Alpine has been moved to the H2 (RWD) class (made up of the previous game's 1970s cars), where it replaces Lancia Stratos, that is now competing against cars from the previous game's 1980s class in the H3 (RWD) class.
Also from DiRT Rally, Peugeot 205 Turbo 16 Evo 2 is very much this trope in Difficult, but Awesome form. While it's easily the hardest 4WD car in the game to handle (being the most powerful rally car in the game and all), it wipes the floor with the rest of Group B cars once you learn to use it properly.
Tear Jerker: Beating the Colin McRae challenge in DiRT 2 treats the player to a short tribute to Colin's rally career.
The Monte-Carlo Rally, DLC in DIRT 3. To elaborate: Most stages in the game are wide enough to fit at least two cars side by side. This rally has sections where only one car can fit, and it's a tight squeeze. It's not much easier in DIRT Rally.
In DiRT Rally, pretty much every single track can become this. Justified, though, being a Nintendo Hard game at its core. In 2.0, however, Argentina has received the most fear from the players, being a rally full of tight courses with massive rocks and boulders scattered throughout the sides of the road.
DiRT Showdown is viewed as such by a number of players who are understandably fed up with the "dudebro" attitude espoused by the previous games. It took out the traditional rally modes and replaced it with demolition derbies involving Fauxrrari cars.
Same went for DiRT 4 whose handling model is a single point of contention amongst sim racing fans.
Win Back the Crowd: How many of the fans view DiRT 3 and DiRT Rally, especially after their dissatisfaction over Codemasters pushing for too many arcade-y or gimmicky elements in DiRT 2 and DiRT Showdown.