Somehow, Japan always brings some of the greatest gems ever into the world, like Super Mario Bros., Sonic, Final Fantasy, and other epics...And yet here we go, another epic pops up somewhere along 2004.
I might as well give you the exact description Pixel, the [sole] developer of Cave Story, gave for his game.
QuoteCave Story is a jumping-and-shooting action game.
Explore the caves until you reach the ending.
You can also save your game and continue from where you left off.
Although it may seem simple, this game is far from it. The actual gameplay itself is very reminiscent of the Castlevania and Metroid series, as it has been compared to commonly, positively. Pixel worked on this masterpiece for a total of five years, and what came out of it was one of the most addicting and best Freeware games ever.
There is an actual storyline to this. You are stuck on a floating island. You're a robot who, to just simply put it, got struck with amnesia. But it is soon that you learn a new ruler has arrived on the island and is plotting to rule the world through an intricate plan requiring red flowers. The premise may seem stupid, but I'm removing some key points.

What makes the best part of the game is some of the difficulty. It's not totally frustrating, but you would need some deep platforming skills. The final secret level, the infamous Sacred Ground, is absolutely brutal and can basically rape your butt if you don't know how to consistently keep yourself unhurt the whole time. I prompted myself to post this thread after beating the stage...which took me...a week or so...to finally defeat.
Game Screenshots:
The game is also coming for the Wii on WiiWare. The game had a whole Vectored graphic change, and I must say, it looks dazzling. The music is also remixed, but fortunately it is a toggle feature (In Cave Story, the music is 8-bit).
WiiWare Screenshot:
Download:
Cave Story Deluxe Package (Contains automatic English patch)Cave Story (Macintosh Version) (JP)Cave Story (Macintosh Version) English Translation PatchCave Story (Linux Version)
If you already have Cave Story and have beaten the Sacred Ground with the Nikumaru Counter, please post your time here!

The time I just got is a slow 9'00"3. :/ But hey, it's my first time beating it...Playing it safe was always a good method.