DSi-enhanced game cartridges are DS games that have additional features when played on the Nintendo DSi or 3DS. Black, White, Black 2, and White 2 can connect to WPA and WPA2 protected wireless networks and utilize the camera when using the Xtransceiver when played on a DSi or 3DS. However, they are also region-locked on these systems.
According to Bulbapedia, like, the biggest Pokemon source ever (xD) that is pretty much all. Just more availability to internet connection and using the camera for the Xtransceiver. Not even I knew that. :o
Hope I helped. :)
EDIT: Just to clarify, the 3DS share the same features. Also, wireless connection is a lot easier if you've hooked up the connection and what not. You just have to switch the wireless switchy thingy on the side of the 3DS and the C-Gear will turn on. That is the end of the edit. :3