When reviewing Worldwide Karts, one must take into account that this game has been developed by a student as his final project. Obviously, he doesn't have the technology and resources of big company games but despite that, I think he has achieved quite satisfying results.
The game is played in a small window (no possibility to resize, I reckon) and enables you to play a single race or join a full championship in six different tracks.
Karts are quite difficult to control at first, as they tend to skid out of the road all the time, but races are generally quick and fun, including ramp jumps and obstacles to avoid (or crush intentionally).
On the downside, the game quit to desktop every time we tried to test a multiplayer race.
One last thing I really missed was the possibility to customize my pilot (I couldn't even change the name) or choose between several karts.