It's a fair question...I will do my best to answer, others please chime in with anything I may miss:
1.) Online gaming! Pokemon Battle Revolution is only the first of many forthcoming: Mario Strikers Charged, the new football games (I think - I'm pretty sure Madden 08 is Wifi), Super Smash Brothers, and others will allow you to play games against people across the world. As I've said before, if all of them are as easy and flawless to connect as Pokemon, this is going to be a fun year!
2.) With the internet channel, you can play the above flash games, obviously, through the Wii, using your Wiimotes
3.) Google videos (as well as others) that are flash driven are now also viewable using the Wii internet
4.) Sharing Miis with Wii friends via your Wii codes.
5.) For just the fun of it. Now you too can check weather, sports scores, etc. on your TV instead of your PC.