From Wikipedia:
It has similar gameplay to past titles in the Cruis'n series; players race down one-way courses consisting of streets (based on real-life locations) while avoiding various road hazards such as oncoming traffic and constructions. Players can gain a limited temporary boost in speed by using nitrous oxide, otherwise known as N2O or simply Nitrous.
Cruis'n, like its arcade counterparts, allows players to customize and upgrade their cars' features, such as spoilers, decals, neon lights, ground effects, and engines, which they must purchase with money earned from races.
Cruis'n contains twelve courses which can be raced on four different difficulty levels.