I personally don't mind the GBA slot being removed since I always found it slightly annoying to have to see my GBA game cartridge's ass hanging out. The camera both confuddles and intrigues me. The bigger screens excites me.
The DSi [or as some people are nicknaming it, the iDS] is basically Nintendo's answer to Apple's iPod, but I don't think I'm ever going to use the SD card feature for music. I suppose it'd be a decent contingency plan whenever my iPod's battery dies, which happens often because I always forget to charge the silly thing. Lawl.