Man, I love Kuma, Ganryu, and Wang. But I only like Christie for eye-candy, as she plays like crap (to me) and her stories tend to be lame.
Devil Within was painful to beat (each stage took me at least 30 minutes), but beating it will get you a lot of stages selectable, Devil Jin playable, 1 million gold, and Evil Symbols in each stage. An Evil Symbol will give you an expensive (500,000G) customization.
I'm trying to beat the game with all the characters before I get GB Rush (I can't multitask games). So far I think I've beat it with nearly half, and I have to say that Craig Marduk has the WORST ending yet.
I love the cusomization too. I gave Heihachi a hard hat and an eyepatch, Ganryu the samurai hat and Blues Bros. glasses, Marshall the chef's hat, ladle and frying pan (fighting chef!), and a lot more custom stuff I can't remember.