Maybe it's just me, but I don't like the way Mario Kart 8 looks. I feel like the environmental effects, and overall track design look too realistic for the cartoony character models.
I like that about it. It looks like figurines racing. It's what Smash Bros should look like seeing as how it's actually about figurines fighting. The game is impressive for the hardware considering it runs at 720p, 60fps, and it look like that, especially compared to the Sonic or Modnation/LBP kart racers.
as for what changes to make with the series, look at diddy kong racing, crash team racing, or either sonic kart racer. not saying it needs to make those changes. the mario kart series does well using its same formula since 92.
and while I'm bummed that nintendo is embracing its new hardware by making the same old games with better graphics, the last mario kart I spent time with was mario kart ds about 8 or 9 years ago. I might be interested in getting mario kart 8.