New firmware, built in web browser, WEP support, DSiWare games, DSi Exclusive games will have better capabilities then the current DS.
Alot better upgrade then the Phat to Lite upgrade that alot of people did. The Phat to Lite did what? A brighter screen and smaller design. Oh, and lets not forget the fact that GBA games stuck out. That cost $130. With this you get MUCH more features then the NDSL.