An Untitled Story
http://www.mattmakesgames.com/showgame.php?id=13
http://www.mattmakesgames.com/games/AnUntitledStory.zip
PC (Windows 2000/XP/Vista), Keyboard or Gamepad
"In An Untitled Story, you begin as an egg in your nest, and the rest is up to you to figure out. Fight 18 unique bosses, traverse a huge game world, and unravel a mysterious storyline. The single player game features non-linear progression and 5 difficulty levels for extra replay value. Also included is Heist Mode, a multiplayer capture-the-flag-style versus mode. Hook up a USB gamepad before starting, to play it as it was meant to be played."
This is the single best freeware game I have ever played. It is a Metroid-style (and I don't use that lightly) game with platforming elements and a unique design. The game was designed, programmed, drawn and composed by the same person (Matt Thorson), so everything ties in really well.
An Untitled Story is a single game world with non-linear progression and upgrades are placed around the world that allow you to reach new areas constantly. There is a story - you just have to find it yourself during the game. It can be very, very hard at times, but it is so enjoyable and non-linear that you'll never be frustrated. The game is full of small discoveries, whether that be new areas, upgrades, bosses or just hearts in hidden alcoves.
The art style is truly unique. It is hand-drawn, but the effect is incredible when put together. There is no repetition, anywhere - each area has unique rules and mechanisms. The music is simple, and fits the areas very well, but the tunes are extremely catchy and rivals Nintendo's best music in some cases (and I only like Nintendo music, so again that's not exaggeration).
It's free, and very easy to get into. It is a primarily single-player experience but has a fun, short local multiplayer mode. The game is quite short (It's a one-man production), but discovering everything and getting good enough to progress takes a considerable amount of time. The higher difficulty modes add a large amount of replay value.
Try it. You WILL love it.
http://www.mattmakesgames.com/showgame.php?id=13
http://www.mattmakesgames.com/games/AnUntitledStory.zip