Although I totally enjoyed Zero, my main gripes about the game was unlocking the highest level parts available for body tune, engine and mufflers. While you will most likely get the parts before you finish the game like let's say, there will always be that one car you're going to be using a lot, if you wanted to get those parts for your other cars, this is probably going to take you weeks. There is a trick to obtaining it like leaving your game on while on the victory results menu or whatever for 30 hours without exiting the menu which I did use to get the parts for my R33 so while you're waiting until the time comes when you hit 1864 miles, you could be doing something else like watching a movie, playing on your other game consoles or go out and do stuff. Still I just think it's sort of a pain to do this for every car rather than doing it for one car and then the parts will be available for every other car in the game.
Another thing is that once you finish the game and you've already spent all your millions that you got from beating Speed King and White Charisma, *no you don't get another million dollar bonus for beating Unknown* the game becomes a big grind since all the races you do will always pay you $1k. Although if you're concerned about this, best thing to do which I would only recommend if you already beat Unknown which in other words, you would already have beaten the game, you could continue playing the game from there without saving so you can try out all the cars and there upgrades, visual modifications, etc. with the exception of the level 5, 7, and 8 parts for the engine, body tune and mufflers since there's no way you're going to be leaving your game on for over 30 hours. Regardless of those 2 flaws, the game is still good though. The game did have some interesting cheats which I would like to point out.
