This is a game that is truly fun for everyone, and will keep you playing for a long time.
First, I'll talk about the customization. This game is the second installment of Sony's "Play, Create, Share" genre; LittleBigPLanet being the first. Although i never played LBP I have heard that the customization was very difficult in that game. In Modnation, that is definitely not the case. You can create your own characters (Mods), Karts, and even tracks. All of the creation tools are easy to use and the possibilties are endless. You can make simple creations that take no more than 15 minutes, or you can spend hours perfecting your creations. On top of that, you can share your creations with everyone else with the game, and you can dowload things that other people have made.
The ability to make anything you want is great, but if the actual racing wasn't fun this game would be trash. Fortunately that's not the case. Unlike MarioKart, or other similar games before, Modnation adds an element of strategy to the races. All of the items have three levels and you have to make the decision to either use it right away, or wait to upgrade it for a more powerful attack. Also, you have a boost meter that you build up during the race. You fill the meter by doing things like drifting, drafting, and doing tricks. When the meter is full you have another choice to make; it can give you a speed boost, or it can shield you from incoming weapons. The karts handle well and the racing is just plain fun.
If I had to say something bad about this game it would be that there isn't much variety with the weapons. There are only 4 starting weapons and then you go on to upgrade them. This is only a minor problem that doesn't bother me too much at all.
Overall, this game is awesome! I have already pre-ordered my copy and cannot wait for it to arrive on Tuesday. I definitely recommend this game to everyone.