Though it takes more effort to install than a typical game, it's well worth it, as I love it, and everyone else I know who's played it also loves it. The only reason I'd not consider it necessarily better than _Metroid_ is because Metroid came first. (Doukutsu plays a bit like it, while still being very original. It also has a very good story that plays out as you proceed through the game.)
I'd tell you more about it, but it would be really hard to do so without giving away important plot elements. Take my word for it, though, this game is _fun_!
Here's the page of OS X software by Pixel:
The DL is the link under the top screencap, labled: ダウンロード(1.6MB)
Now, since the translation program is a Windows EXE, I've uploaded the translated data folder in a zip file for all here to download as needed:
(Credit goes to http://agtp.romhack.net/ for the translation.)
Unzip data.zip, then, after installing Cave Story (Doukutsu), control/right click "Doukutsu.app" (or Doukutsu if you don't have it set to show the extension) and select "Show Package Contents". Copy the folder 'data' that you got from unzipping data.zip into Doukutsu.app/Contents/Resources. When it asks you if you want to replace the existing data folder, do so. You should be able to play it fine after that, and it's well worth the effort!
tab = toggle fullscreen/windowed mode
Arrow keys = movement
down arrow = use/pick up object, door, etc.
z = jump/confirm
x = fire
a = previous weapon
s = next weapon
q = item screen
w = map (once map system is acquired)
escape = pause (F1 to resume, F2 to reset, escape again to quit.)
Also, as it was originally a Windows game, if you've got friends who use Windows, they can get it here: