The only graphical flaws that impacted the game's final score were the issues caused by split-screening:
- 30 FPS during 3 & 4 player races
- no option for a horizontal split-screen
- no option for GamePad gameplay during multiplayer
- visibility problems during sharp turns and anti-gravity sections
The frame loss (59 FPS) and accompanying stutter effect whenever AI drivers are involved is definitely noticeable, but ultimately not a big enough issue to have any impact on the overall score. Same thing with the lack of anti-aliasing.
The main reasons I gave Mario Kart 8 a 7.5 score are the coin system, the poor weapon balance, the bungled Battle Mode, and the lack of any new single-player content. Other issues like a weak character roster and limited online voice chat contributed to my negative impression of the game, but did not affect the final score significantly.
After the gameplay flaws, the biggest issue to me is how Nintendo has not introduced one new single-player mode in over 20 years of Mario Kart sequels, which is unacceptable, when kart racers as old as Diddy Kong Racing (1997) and as recent as Sonic & All-Stars Racing Transformed (2013) have proved that it's possible to have interesting single-player modes as well as a compelling multiplayer experience.
Sonic & All-Stars Racing Transformed, in particular, includes everything Mario Kart 8 has (Grand Prix, Time Trials, co-op, online play), but it also features a huge World Tour mode that I still haven't beaten, after playing the game regularly for more than a year.
There's no excuse for a Nintendo-made game on its eighth version to be shown up in that regard, especially by a series that's only on it's second sequel, and is operating with a much smaller development team and staff budget.
As for why the game scored as high as it did despite all the criticisms mentioned in the review, Mario Kart 8's multiplayer experience is still extremely fun, especially online -- the netcode is some of the best I have ever seen in a console game.
For the same reason that we review titles like NFL Blitz and NBA Jam:
Mario Kart, even with its fantasy power-ups, is still a racing game, just as Blitz and Jam are powered-up versions of football and basketball, respectively.