http://www.cavestory.org/OR
From Wii Shop Channel
No, this isn't a private server. It's a freeware game that was made back in 2004. You've probably heard me talking about it at one time or another, and it's in my Sound.wz.
It's a pretty awesome game, and would be a great thing to do if the server is down. (Which apparently has been happening quite a bit lately)
Somewhat of a mash of 2D shooting, platforming, adventure and (vaguely) RPG.
The game has a pretty awesome soundtrack, hidden elements, a touching storyline, and the highest replay value of any game I've ever seen.
You have every reason to play it.
My best times on the Speed-run sections of the game are in my signature, if you wish to try and best me.
(Boss rush time is on the Wii, btw)