One thing about that online mode: it features a nasty bug that can completely ruin the experience, but is incredibly easy to fix. If your online games are plagued by loads of lag and a horrible frame rate, head out to the Xbox 360 dashboard and slide over to the "System" blade. Click on the "Computers" option and disconnect any PC listed there. Voila! Problem solved. Note that you can still use custom soundtracks in Ridge Racer 6 while playing online, but they have to be run off the hard-drive or a USB device such as your iPod or PSP.
Ridge Racer 6 didn't get much attention at 360 launch, overshadowed by the amazing driving sim Project Gotham 3. Ultimately though, you shouldn't look at these two games as adversaries, but rather as two hot rods that should share the same shelf. Both offer a completely different experience, and both excel at what they do.