These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: The whole "two drivers at one time" mechanic. Either it's one of the most innovative features to be introduced to the entire Mario Kart franchise and needs to make a return, or it's one of the worst aspects about Double Dash and it's a good thing it has yet to be brought back. There are also those who were completely indifferent to the whole mechanic, but there have been some debates among fans of the first two camps on if the feature should or should not return in a future entry.
Franchise Original Sin: in Mario Kart 64 and its GBA successor, Super Circuit, the Spiny Blue Shell worked like a red shell, but it hit every driver in front of the one who threw it and finished with the one in the first place; this game, however, marks the debut of the (much more hated) flying version of the item, that only hits the first-place driver with an explosion that takes five to ten seconds to recover. By the time the first-place driver is back on track, the second-place driver is likely to have already surpassed him, and usually said second racer is the only one taking any advantage of the weapon. It took Nintendo two more games (Mario Kart DS and Mario Kart Wii) to either realize the mistake themselves or to notice the item's infamy among fans before reverting the item to its non-flying form (while still exploding when hitting the head racer) in the series' Nintendo 3DS outing, Mario Kart 7.
Hilarious in Hindsight: On one of the promotional websites for the game, Lakitu mentions that although he's been in every single Mario Kart game, he's never been a racer. Then Mario Kart 7 comes out, and he's an unlockable character.
Magnum Opus: The franchise's former one. It got dethroned by 8.