Continued from other comment..keep engineering behind the first game, mix it with this one, with LOTS of upgrades with a BIIIIG challenge. maybe not right off the get go but a few tracks in make it REALLY hard and give it some badges.
this game has a LOT of potential. i would actually pay money for a game like this on the xbox. just simple fun. the first one was really really good. imo the graphics and the feel to it was WAAAY better. adding in 2-D girls is a little too cheesy. also, in the first one it was almost like upgrading your handling was bad... maybe once or twice but no more then that. it looks like the game was a little half-assed if you ask me.
imo i think this game would be awesome if:
1. buying cars was an option
2. upgrading available via money from winning, or some other way
2.b and not just speed, handling, accel, and little things like that. take the time to draw out suspension parts such as rack and pinion or leaf spring options. look at the upgrades for IDAS4 and just do something similar. make it hard to upgrade, but not impossible achievements.