A funny kart racing game which is missing something to make it good.
The variety of characters is really good. You will have over 20 characters to choose with, including Sonic, Tail, Shadow, Dr.Eggman, Ryo and Amigo. In the XBOX 360 version, you will also have Banjo & Kazooie. If you want to pay an extra, you will also be able to purchase Sonic Metal. I don't think that it worth it though since you already have a lot of characters.
You will have about 5 themes of track which all contain about 3 tracks each. You will not be able to race them backward or mirrored though. They are nice and several of them contain shortcuts that are really shorter, so you will have to take them if you want to win.
The weapons are more or less the same than in Mario Kart. You have a shield, rockets that are auto-targeted, bomb that goes only straight ahead/behind and few other ones.
There is a mission mode which include 64 different missions that are more or less the same. There may be 10 different missions. They may be pass trough checkpoints, hit the opponents, races, etc.. Toward the end, they really get very hard.
There is also a time trial mode that does not need explanation.
You do not have have any championship mode that worth playing. It only shows a short cut-scene with the characters on the podium. There are not real rewards for doing them other than unlocking the next championship.
You will have some musics, characters and tracks to unlock and after that, you will have nothing to do with your cash.
The achievements are bugged and reset very often. If you plan having all the achievements, plan to lose a lot of time redoing the same achievements.
Online racing is nice. There are still few people on it so you can have a good challenge against other humans.
Globally, this game is not as good as it may look at first glance. Few hours can be spent on it, but after a certain time, you will get bored of it because of the several bugs that are in it. If you can find it in the bargain bin, ok, if not, do not spend any money on it.