All or Nothing: The Arcade challenges provide an example: either you achieve the objective and you gain Kudos (the higher the difficulty, the higher is the Kudos quantity received), or you go home with nuthin'.
All In The Manual: The manuals for 3 and 4 are chock of infos about the game, but the former is more comprehensive: it even goes as far to talk about the huge soundtrack, with even a few examples from each playlist.
Disc One Nuke: In 4, Quick Race mode and the Driving Test will give you all of the hundreds of cars in the game right off the bat, so you can test them all and find the ones that fit your style... And even test out the Ferrari F50 GT.
Dynamic Difficulty: On normal and hard difficulty, beating the AI will be nearly impossible if you mess up too much in career mode.
Rubber Band AI: On the other hand, you have to be nearly perfect to beat most of the AI in higher difficulty if you want to win the races.
Driving Test: The Michelin Test track for trying out any car in PGR4. From the straightforward oval circuit to the Ultimate Test, the player can measure any of the cars and bikes in the game (in this mode, all of the vehicles in the game are available from the very beginning) in three tests: a time trial in any of the five layouts of the test track, a speed run in the oval circuit, and a solo drift contest.
Cool Car: The A car class breathes this trope. Nothing else than non-road-legal race cars and hypercars. If you ever race in this class, get ready to see a free-for-all brawl of badass race cars to see who's the best on the track.
Infinity–1 Sword: In 3, the Mclaren F1 LM, the Mercedes-Benz CLK-GTR Supersport and the Panoz Esperante GTR-1 are this to the godlike Ferrari F50 GT.
Killer App: 3 was definitely one of them at the launch of the Xbox 360. 4 could've been one of them, if it wasn't for Forza Motorsport 2, which has exited at around the same time as PGR4 and stripped the killer app title from the game.
Level Editor: 3 interpreted it in a different way: there is a special mode called "Route Creator" where the player is able to create his own circuit by putting checkpoints in the various roads in the 4 main scenarios of the game (London, Las Vegas, Tokyo, New York City).
Fixed in 4. The championships in the Career mode can net you several thousands of Kudos, and in some cases, you earn enough Kudos to buy certain car packs containing a set amount of cars including the Ferrari FXX, Lamborghini Murcielago, and even a FREAKING Mclaren F1!
Loads and Loads of Characters: In PGR4, the AI on career mode have human names, and they all have different personalities: some are more aggressive and concentrate on pulling out tricks to get more Kudos, others are more focused on true racing.
While the Project Gotham Racing didn't contain as much cars as Gran Turismo and Forza had, PGR4 managed to make wade variety of car production years with more than 130 cars from the 1950s to 2008.
Alot of these cars have yet to see an appearance in most sim racing games.
Nintendo Hard: Platinum difficulty. Oh god: in this difficulty setting, the AI will always be on the back of your neck, and the objectives in solo challenges require nigh-inhuman skills to beat. The latter example is much stronger in 3: in style challenges (where you have to gain a determined amount of Kudos with certain moves to win), in Gold difficulty you sometimes have to reach a few thousand Kudos, but not that much to be Nintendo Hard. In Platinum? You have to beat an objective which is FROM 3 TO 10 TIMES BIGGER than the Gold difficulty one!
Racing Game: Well this is Project Gotham Racing after all.
Rare Vehicles: The Caparo T1 in 4. The thing is a street-legal Formula One car, basically. Only 25 are churned out a year. As of 2012, only 16 have been sold.
Reality Is Unrealistic: Almost every game in this series warned players that the depictions of the game is unrealistic despite the fact that each game showed semi-realism such as breaking for turns instead of speed-turns, etc.
Scenery Porn: The city buildings in PGR4 look absolutely stunning even by today's standards.
3 and 4 both detain a Guinness World Record: "Most Complex Scenery in a Racing Game", with New York City. Just the Brooklyn Bridge ranks up at over a million polygons and an half.