7 is definitely the best of the series, but the improvements it brings to the table are probably going to be unnoticeable to anybody who judges the game based on the GP races by itself. Things that come to mind after an absurd amount of time with the game:
-Best online implementation I've seen in a console game; the whole way that everything you do contributes to an online ranking was great. What *wasn't* great is that Namco didn't patch an obvious exploit, leading to the ranking graveyard you see today. I really wonder why those guys didn't think they might have to do some community support.
-The parts system and drafting fix every problem I had with Ridge 6 and Ridge PSP. Now you don't have to race absolutely perfect to do well, and the parts types let you choose your own way to drive, rather than being stuck with "Angelus or else". It also alleviates a lot of the grind, because the rewards are actually tangible as opposed to the weak "new mode" stuff or minor paint jobs released.
-Art style was improved significantly; go back and play Ridge 6 and you'll wonder why every level has dark storm clouds and half the brightness.
-Unlike Ridge 6, you can actually play the DLC music tracks at any point in the game. (Ridge 6 restricted you to choosing before the race; you can't select DLC music during the race...ughhh)