I've been playing Mario Kart for quite a while. I didn't play Mario Kart 64, since by the time I was functional enough to enjoy it we had had Double Dash, but I played quite a bit of Double Dash, Mario Kart Wii, and finally Mario Kart 8. I didn't play the handhelds purely because I didn't have access to them. I played Mario Kart Wii so much I had probably around sixty percent of the expert staff ghosts beaten. It doesn't sound impressive unless you really know how difficult some of those times were to beat! As a side note, I never really played online on any Mario Kart game. I spent a lot of my time on Mario Kart Wii and Mario Kart 8 getting the highest possible ratings on the single player aspects of the game.
So with the introduction of anti gravity and a few new items, I was pretty excited for Mario Kart 8! I was completely, utterly, thoroughly disappointed. Virtually every change they've made to this game was a step in the wrong direction.
First, there are pretty much only two new things I liked about Mario Kart 8. The first is that I will admit the anti-gravity courses does make for some interesting gameplay. It's sad that it doesn't feel any different from normal driving, but the maps definitely get more interesting when you can make the tracks defy physics. It was a great idea that I think could have been implemented better, but doesn't suck. Second I like the idea of 200cc, where everything is going almost uncontrollably fast. I haven't played on this setting very much, but obviously you don't have to play at this speed if you don't want to. Still, I think giving more freedom of choice to players so that they can manipulate variables how they want makes it more fun.
That's all the good I have to say for this game, though. They took out a lot and changed too much for me to enjoy it. First, in order to implement the anti-gravity and make everything its own game, they made dozens of new maps. It sounds cool, but in the past (like in Mario Kart Wii) half of the courses were retro maps that were in older games. In fact, almost all of my favorite tracks in Mario Kart Wii were tracks that were in older games. It makes it so you can play on the thing you remember and love with new twists (like new items or whatever). In Mario Kart 8, though, all of these new maps were changed. Some are reminiscent at best, which means I simply don't like any of those maps because they feel like mockeries of what could have been. I find this odd, because they spent so much extra work making something new when less content in the past worked!
Next, the game itself is a lot simpler. Most Mario Kart courses in the past had shortcuts you could take that would slow you down if you didn't have the proper item (i.e. mushrooms) to boost past it. This game doesn't have a whole lot of that, meaning getting those mushrooms when you're losing sucks because it could easily be something that could help you out more. You can't use that mushroom to skip part of the level and catch up anymore. As far as simplicity goes, too, I liked the differences between karts and bikes. They feel and drift different, but in this newest installment they are largely the same. In Mario Kart Wii, you can drift more on a kart (getting first blue and then red flames for a nice boost). In a bike, you can only drift for the blue flames, meaning ostensibly that you can't benefit from boosting as much as karts can, but bikes can also do wheelies, which makes them go faster at the cost of being able to turn. This means that they would make up for their speed on turns by going fast on straightaways. This is all removed in Mario Kart 8. Also, coins? Why was that a necessary addition to a racing game??
Lastly, Battle Mode was my favorite part about playing with friends. Jumping into arena shaped maps and actually trying to attack each other was way more fun than racing in previous games. It was mostly one of us would simply be the best at racing, so there was no point in trying to compete. But in Mario Kart 8, there are no arena maps. When you go into Battle Mode, you simply go onto one of the real tracks and battle there. This doesn't work nearly as well because its no longer an arena. I actually don't understand this choice of development at all, when they could have simply thrown in the arena maps they used in the past if they didn't want to make new ones.
I could be biased because I remember how good I was at Mario Kart Wii and hold this new one to an impossible standard.