My first reaction: "Why?"
There are precisely nine billion Mario Kart wannabes in the universe already, so why do we need one starring various Sackboys? What's more, even though you could safely assume that there'd be a ton of customisation in this particular kart racer, didn't Sony already do that with ModNation Racers?
A hands-on experience with an early version of LittleBigPlanet Karting didn't really answer those questions, but it did show itself to be a reliably fun kart game, ticking off all the boxes you'd expect from such a respected IP: tight controls, integration of various LittleBigPlanet-themed worlds and in-level objects, a variety of weapons, and so on.
There will be a wide assortment of worlds to race in, cherry picking from previous LittleBigPlanet games as well as introducing new ones. You can play with up to four players locally, eight players online, and - I always like this one - two players locally versus a bunch of others online.
That's all well and good, but still: Why? The answer to that comes, perhaps unsurprisingly, via the level creation tools that are a hallmark of the LittleBigPlanet games. They're looking impressive here: it's basically the fully-featured tools found in LBP2, only now in the third dimension.