I've been looking for a decent kart-racer for a while now, and i think i've found it.
Racing Transformed has garnered some great reviews, and after watching some gameplay vids, i decided i'd give it a blast. It's a very well made game, and pays homage to the various Sega franchises in a really respectful and detailed way (I particularly like the first Shinobi track - sooo nice looking).
The racing itself is, to use a cliche, easy to get into, but hard to master. I like the one-button drift mechanic, and the weapons seem nicely balanced and not particularly skewed either way towards offense or defense.
The titular 'transfomed' element adds an awesome depth to the gameplay, and your vehicles handle quite differently between land, water (or lava on some tracks), and when in flight. The first time i came off a ramp and my machine became a plane was quite a buzz, but the added vertical control dimension was initially a bit overwhelming. You get to grips with that pretty quickly, and after a lap or two the transitions become second nature.
Tracks themselves are varied, with plenty of shortcuts, and they change and morph from lap-to-lap. They also look great; a large amount of care and attention from the developer has clearly been put into their design.
Overall i'm quite impressed with the title, and believe it's as good as any other kart-racing franchise/game.