It's funny how from the very few Xbox games that I've actually played, the ones you ask about are always part of that small group of games
I've spent quite a lot of hours playing Quantum Redshift, mainly because there is a lot to unlock, but also because it is generally fun to play. It has very nice graphics, lots of characters to begin with as well as to unlock, and each character has their own racer pod. By beating the tournaments in various difficulties you earn points which are then used to upgrade every character's respective racer. They each have their own weapons, specialties, etc. Every character has their own respective race course and archenemy as well. Every pair of archenemies has their own nationality, and this is shown through voice acting in different languages and their race courses.
I consider it a quality title, but it depends on where your taste lies. It's basically just a futuristic demolition racer with a lot of extras for added replay value.
-Speedy