I just recently learned of this little: dare I say gem?..today after reading the latest Gameinformer! While it’s at least 1800 Wii points on the Wii shop channel; the PC version is completely free and just as compelling!
If I had to compare it to any number of things I’d Say: It’s the offspring of Knytt stories (another awesome series of games) combined with Metroid-like weapon system advancement and exploration, mixed in with more than a touch of Castlevania! Does that sound good to you! 
Here is the download link. Make sure you get the Japanese version along with the English translation:
miraigamer.net/cavestory/downloads_1.php
There are some differences though:
The Wii version has updated graphics but has missing and changed music, compared to the original. Oh, and worst of all: the Wii version has a number of crashing bugs.
Other than that, I’d say: if you already haven’t played it, there is nothing to lose and everything to gain from playing this wonderful retro-hearted gem!
I’m pretty sure you can set the music to classic on Wii. Unless you mean it’s a bug that makes it missing. Yeah it seems they did a sloppy job in the end, but hopefully they’ll fix it. No wonder it kept getting delayed and not passing Nintendo’s approval.
The Wii version has a couple extra modes as well though. And hey nothing stops anyone from playing both, personally I think Pixel deserves it to be a success and will buy it soon, even though I’ve played the original release.
And since we’re talking of indie gems going WiiWare, Noitu Love 2 is also coming up, at some point. Great little eh, not quite shooter, not quite beat em up, from just one dude again. This one’s not free on PC though, $10. Paid for it ages ago, loved it to bits. The Wii version will probably cost similar. Also, play the dude’s free Zelda homage.
And then there’s La-Mulana, which is closer to Cave Story I suppose, and is an awesome homage to MSX titles. Intentionally clunky and tough as hell but awesome. The Wii version will be more user friendly and, well, much prettier, ditching the MSX style for something more akin to SNES. The PC freebie can be found here.
Finally, Super Meat Boy is a masochistic platformer sequel to a free flash game, coming to WiiWare, Steam and XBLA. I liked the flash game quite a bit, the sequel certainly looks promising enough and also has a level editor, but who knows.
