Stolen off NeoGAF:

If you have Cave Story on WiiWare, go to the shop channel, find Cave Story again, and select the Update button.

At the least, the remixed music has changed, and the map overlays on top of the game screen, rather than going to a black screen.  Some other changes might also be present.

They changed the music? As in they added the percussion tracks to it?

...suddenly, all is right with the world.

Is it out in Europe yet? Please, I cannot take this anymore :(

Not yet, but supposedly it's coming soon.

It's Q4 in Europe.  At the last update they said they were doing some final testing for the EU release.

That they've now updated the US version tells me they've finally finished and hopefully they'll release it sooner than the very end of the year.

I got this update earlier today. I only played past the Egg Corridor, but I do intend to play more.

The music is definitely improved. The Cave Story theme sounds natural when it has "bounce" to it. My favorite song in the game, Arthur's House, is even better. Aside from the music, they also fixed at least one of my major nagging points about the game, specifically the XP chips. They're no longer obnoxiously loud when there's a whole bunch of them bouncing around. I'm going to be looking forward to this playthrough.

My only complaint is that the fixed music hasn't been uploaded onto Youtube yet so I can indulge if I feel like it.

Nice! I'll go update. Cave Story is one of my favorite downloadable games, right up there with Flower and Wipeout HD.

I've been waiting for the WW version to hit Europe for absolutely fucking ages now

I thought there was a free PC version that plays on just about any non-ancient PC? Or is this version somehow better? (Honestly, I don't know.)

Updated music and graphics, as well as extra modes like a time attack and boss attack mode.