It's... mediocre, I guess.
It sure is beautiful and sounds really good, but the controls are kind of difficult to get used, and there's just too much gacha elements.
It it feels like Mario Kart, but really dumbed down. It could be much better, for sure.
I edited this review because I played the game again, for a longer time, and got bored pretty easily. I was trying just to finish the game and get back to my life when I discovered that the game has no ending, the cups are changed every two weeks.
This is outrageous and now I hate it so much.

(Review was made in 2019 and may not reflect the current state of the game)
Mario Kart Tour implements a lot of features that make the game work for a mobile game. The points-based system rather than a straight up race adds a whole new layer to the game, making every little action feel important. The way that different courses have different favoured characters/karts/gliders means that no one combination is ever the best, and unlike the actual MK games, you'll find yourself making use of the wide variety the game gives you.

Unfortunately, and it's a big one, the game is awful from a gacha standpoint. The amount of premium currency you get as a f2p is some of the worst I've ever seen in a gacha game, and they have a subscription based service which gives you not only extra unlockables, but even unique karts and gliders.

The game has a coin shop which is pretty neat and allows players to buy what they want when it shows up, rather than relying on RNG. Unfortunately the gold-pass unique items and even the spotlight items will not be included.

The way that banners are done in this game is also very greedy. Each banner has a total of 100 items inside, which includes the spotlight items, and one other random ultra rare item of each type (character, kart, glider), meaning that you might not even be able to pull the item you want. While each tour is 2 weeks long, the banners only lasts only 7 days, and then it swaps out for a "new" banner, which is the exact same banner, but with the spotlight character changed, meaning all your pulls from the last pipe are reset.

Controls are awkward, as you can imagine with a mobile racing game with a ton of drifting and item usage.

There was so much potential for at least a fun mobile game here, but instead they chose to go for the worst option for a f2p game, locking things behind a paywall and making it as unfriendly as possible for anyone not willing to whale on it.

Mario Kart Tour is a mixed bag overall for me, so I'll jump straight into what's good about the game and what's bad about the game.

What's good about Mario Kart Tour?

It has the best roaster of any Mario Kart game with new comers like King Bomb-Omb, Paulina, Coloured Birdos, debuting as character and has returning favourites.

There is no Mirror Mode in this Mario Kart, but there is better with both Backwards tracks Remixed tracks (sometimes called Trick Mode). Backwards track are not at all similar to Mirrored Mode from previous Mario Karts, it's where you backwards on a track with the track having slight tweaks to make it possible to play. Remixed tracks is where courses are heavily altered (like SNES Rainbow Road) which completely changes them slightly (like DS Airship Fortress) with extra ramps added in which cause a slight divergence off of the main path.

The game (as of October 2020) gets constantly updated with an update once every two weeks usually with 2 new characters (usually reskins of already existing characters like Mario or Wario, but not always), the track rotation changes though new retro courses aren't adding in (only swapping from a handful every time), and sometimes a new track with variations of it (though not always).

The gameplay is controversial to some players, but I feel like the change of focus from traditional Mario Karts which focus on racing to a more "aim for the highest score" is a good change for mobile, as it encourages player to keep on trying to aim for the best possible score over trying to win, which might be hard for those not fully used to mobile.

The controls for a mobile game at least are good, drifting feels natural (holding onto the screen) and using an item requires a tap of the screen which feels natural as well. The game by default has auto-tricking and auto-acceleration on (though at least auto acceleration can be turned off).

The online is free, it used to not be free though.

What's bad about Mario Kart Tour?

The game is GATCHA, which means you get random characters/karts and not necessarily the ones you want by basically spinning by a slot machine in the forme of a pipe/golden pipe (golden pipes are a free spin you get to spin ONCE for beating every track during a "Tour" which come with a guaranteed rare character/item).

As most free mobile games have, this game has microtransactions, but they're extra predatory in Mario Kart Tour with bundles of popular characters like Luigi coming in bundles for FOURTY UNITED STATES DOLLARS (you only start off with a shy guy from the start too), which may make some who are big Luigi fans (my favourite of the two Mario Brothers) feel like they have to buy the $40 pack just to have Luigi. I've played this game for ~2 months in total (2 "Tours" when the game first came out and 2 Tours again recently) and I only got Luigi about a week before I put down the game again.

Another problem with the microtransactions are the rubies just straight up not worth buying, you get 10 spins at the pipe lottery for 45 rubies or 5 rubies for 1 spin individually, but for $3 for you 3 rubies, $6 is 10 rubies, eventually leading up to 135 rubies for $69.99 (more than the price of a first party Nintendo Switch game). Which is 3 spins and you can get duplicates.

The last problem with this game, in order to access features (like an alternative Online mode, used to just be Online in general), bonus items for getting more stars (you get up to 5 at a time on MOST tracks except every fourth one which is something similar, but not the same as a mission from DS' Mission Mode) like extra characters with a subscription service called "The Gold Pass" which is $4.99/MONTH. The game, will sometimes advertise items you cannot get if you don't have The Gold Pass, just to rub salt in the wound. 200 CC is locked behind The Gold Pass too.

The game punishes you for playing for a long time. You start earning less and less rubies the more you play the game, requiring more and more harder tasks to get them, and these are one of two ways to earn rubies without paying for them.

The track selection isn't too great and the new courses don't feel like anything. The retro tracks were most likely selected due to them being easier to render, though there are a few fan favourites, but don't expect to constantly play them due to there being a track rotation.

The rotations are not always timed the best either, unfortunately and don't get cancelled/changed. Like they introduced the Los Angeles Laps during the height of a major fire in California...

The game is based off of Mario Kart 7, so it feels just as face and Mario Kart 7 isn't a fast Mario Kart either like Double Dash or 8/8 Deluxe.

There is no Battle Mode.

So with all of that out of the way, I would recommend avoiding this game, but if you don't have access to a Mario Kart and want to try playing one please don't spend money on this game, it is NOT worth it.

I had fun with it as a major mario kart fan and I'm glad it brought character like King Bob-omb, Dixie, Birdo, and other Mario character that should've been in the actual Mario Kart games, but it doesn't excuse the AWFUL predatory gacha and microtransactions it has. It's has an annoying seasonal pass feature known as the gold pass which lets you unlock 200cc races, unlock badges, and gold races--200cc should've been in the base game but gacha always make weird decisions. In addition to that, the actual rates to obtain what you need such as SRs is rough, and you slowly collect in game currency in this making the grind reward for this not worth it. Controls in Mario Kart Tour are frustrating too.

Nintendo should've never touched the gacha industry and this is an example.

Mario Kart Tour had the potential to be a fun, interesting entry in the Mario Kart series. It really did. I played it when it officially came out, and I was very into it for the first week. Competing with other people for high scores on races was very engaging. It made me play a Mario Kart game in a way that I never had before. However, I got really discouraged to continue once I realized how greedy the gacha system in this game was. I, personally, can tolerate a gacha system when I can earn rewards at a good enough pace without having to dump money into it, but this game just has a terrible drip feed of rewards. Even if you bite the bullet and spend money on the game, the monetary value of the rewards you get is pitiful. I ended up dropping the game feeling more disgusted with it than anything else.

I actually rage at the amount of money this got from me. This had so much potential to be a good game, and good installment to the Mario Kart series that it's actually insane. I can remember everyone in my school with a phone, even those who clearly had never touched a video game in their life, playing this the day it came out. Congratulations Nintendo, you blew it. From the pipe gambling system to pay to win system with certain characters, karts, etc just being blatantly better than others this game really is just a money making scheme for a company with already billions and billions of dollars.