First off... I'd like to say I'm actually not as disappointed as I thought I would be. That said, I can't just summarize the review like that.
Graphics: Impressive... for the 3DS. The lighting is on par with Mario Kart: Double Dash!!, while everything else (even resolution) is equivalent to Mario Bike Kart Wii. Also, it's the first handheld Mario Kart title to not use sprites for items and track objects. Overall I'd say it's a turn in the right direction in this factor.
Sound: I've never been a fan of the soundtrack in the most recent Mario Kart games, but the remixed themes for the retro tracks as well as the themes for Neo Bowser City, Bowser's Castle and Rainbow Road, plus the results screen themes made me have a nostalgia attack (especially since the first Mario Kart game I played was Mario kart 64). I know Neo Bowser City doesn't sound very nostalgic upon hearing it for the first time, but if you listen closely, you can actually hear the theme from Toad's Turnpike in it. I honestly have to say this game has one of the stronger soundtracks in the series. As for sound effects, it's typical modern-generation Mario Kart fare, though I do think Metal Mario's voice clips were lazily made, since most of them are completely identical to Mario's (it makes it worse for me since Metal Mario is my main).
Gameplay: Ok... Rant Time. First off, I hate the idea of hard equalizer items like the Blue Shell of DEATH (interesting how it has the same acronym as the infamous Windows Critical Stop Error's fan-nickname). However, Nintendo did kinda nerf it this time around. It still explodes, it's still almost undodgible (actually, i think they've perfected it this time - I have yet to see a reliable method of dodging this demon), and it travels along the ground like it did in Mario Kart 64, but at least it no longer takes your items from you on impact, meaning that you can potentially defend yourself from getting combo'd now.
Ok... that doesn't seem like much of a nerf, which is my point anyway.
They got rid of the Lightning Cloud and Mega Mushroom, but the kept the Bullet. Honestly, I would have preferred the Mega to stay and the Bullet to be scrapped, because the idea behind the Bullet is fundamentally flawed. They're intended as a way to catch up to the rest of the pack if you're falling behind, but because the only way to fall behind is if you can't drive at all, then it becomes another hard-ish equalizer (the -ish is because bullets tend to drop you off in bad locations, like in the middle of a turn with no edges. Then again I RARELY get these things since I'm usually the guy in first, getting pummeled by blue shells). [/rant]
But then there's the 7. Yes... the 7. If you HAVE to have an equalizer item, then THIS is how you do it. For one item box, you get a mushroom, a red, a green, a banana, a bomb, a blooper (useless) and a star. They're are extremely rare and take a ton of skill to actually put to good use, but they're powerful in the hands of a good player. The three times I've ever gotten one (again, it only appears in lower places), I was able to not only make a comeback but put a TON of distance between me and my opponents. However, most people seem to waste this thing entirely, maybe gaining a single position if any ground at all. Smart use of the "weaker" items in the group is crucial!
Well, sort of... It's possible to snake, but it's not as easy as it was with Double Dash or DS since the drift system is based on drift time. You need a decent amount of track width to get it to work, and you need to be quick on your reflexes and boost as soon as you see sparks before immediately starting the next drift. It's also not much faster than some of the faster cart configurations. Speaking of which...
They finally did it. You can customize your kart, and I'm not talking about simple paint schemes. Probably the best thing about this game is the fact that you can chose your chassis, wheels and glider (more on that later) to tweak your kart's stats. Of course, it's not really worth it to use anything but the Red Monster, Mushroom or Gold wheels, or the Swoop or Paraglider glider wings, but that doesn't mean you have to... that's just the current Metagame scene and you'll see all sorts of combos online. Pipe Frames with the Stardard wheels (Nostalgia Attack again... that's the original kart from Mario Kart 64!) and the Paraglider (because it makes sense), and I've seen all the gold parts at once (Parade Kart from Double Dash).
Gliding is a new mechanic that adds to the game and makes it unique in the series. Take a ramp with a blue boost panel and you are launched into the air. Unfortunately (or fortunately, since it creates a bit of a skill divide), it breaks one or two retro tracks that were updated to have this feature, namely GCN Dino Dino Jungle where a glide ramp allows you to bypass the hairpin right after the long bridge.
Underwater sections have also been added, but I really can't say they're worth much mention.
Storyline: Since there isn't a story (not that racing games need one) I'll use this section to list the new characters.
First off, Waluigi isn't in this one. NINTENDO, Y U NO LIKE WALUIGI?!?!
Now for what they added...
Shyguy is now legitimately playable. Not that he matters anyway. What next... a Goomba? Or what about a Wiggler...
GAH!!!!! Er... Moving on...
In addition to that... thing... we have another... thing...
Honey Queen has been added to the roster too. An unmemorable character from Super Mario Galaxy, I really don't see a reason to talk about her.
Anyway, Lakitu FINALLY gets down from his cloud and competes. Well, it's actually a different Lakitu withb a red shell, but still, it's a nice change from seeing him having to fish you out from out-of-bounds all the time.
Finally, we have Metal Mario. Not very original, but if you're after top-speed then he's your man, er, living metal construct.
Of course, Mario, Luigi, Peach, Yoshi, Toad, Koopa Troopa, Bowser, Donkey Kong, Wario, Daisy, and Rosalina are also in there, having appeared in at least one other Mario Kart game.
Multiplayer: An improvement over previous titles. Now allows for lobbies in both local and online modes. Lag comp is bad though, though the really good netcode reduces lag to begin with.
Modability: I've seen a few cheat codes but that's about it. The e-Shop release might make it easier to do so though, since it's no longer necessary to rip the game from the game card.
Bugs: Hitboxing is a bit disjointed with track objects and items. BSODs will teleport back onto the track if they fall down a pit.
Other: 3D makes this game easier. Also, ergonomic updates to the DS series of systems would be really appreciated, and I'm not just talking about rounded corners.
Graphics: 9/10 if you factor in the limitations of the hardware, otherwise 6/10
Gameplay: 6/10, though Your Mileage May Vary
Story New Characters: 4/10, but if you pay no attention to the giant... caterpillar thing... then 6/10
Overall: 6/10, 8/10 if you consider the current state of the kart racing genre.
Best For: Kart Racing fans, Mario fans, Casual Gamers, Nostalgia, just having fun. Also, some competitive gamers might like Time Trials mode and Online Multiplayer.
Kryptonite: Gaming Hipsters, People who think video games are "SERIOUS BUSINESS", Nintendo anti-fans, CoD fanboys, "Uber-1337 Gamrz", Gaming Elitists, people without childhoods, people who tend to ragequit, the Angry Video Game Nerd.
Recommendation: if you already own a 3DS, are looking for just any game and have $40 USD to waste, then give it a try. I enjoy it (mostly), but I really can't guarantee that you will. I wouldn't recommend going out of your way to get it though.