It's hard to believe this game is free, it's so fun and well made.
From the same creators of Battle for Wesnoth, wich I really like, arises another high quality game:
"Frogatto is a “platformer” or “jump-and-run” videogame. Like in many classic games, the world is viewed as a cross-section seen from the side, and your character (in this case, a small green fellow named Frogatto) walks and jumps between solid platforms, whilst avoiding monsters. We’re not trying to clone any specific game, but we inevitably have a lot in common with other games just by being in the genre. We are trying to innovate a bit.
Frogatto is a finished, fully-playable game. We’re planning to add a bunch of other stuff to it, but we have a complete start-to-finish single-player story you can play right now – just check out our Download page."
Frogatto official site
If you like the game, and wishes to thank the creators, you can spread the word about the game (or even pay $2.99 for the version for iPhone/iPod Touch, if you have one).
There's also a editor in the game, you can acess it with ctrl+e, but I have to warn you to be careful to what you change, unless you don't mind losing your save and having to reinstall the game, if you do some mistake in the editor.
Screenshots below.

I have tried to play that game 3 weeks ago. I hated it. And I usually love 2D platformer.

I like Battle of Wesnoth, I'll try Frogetto!

Why you hated it? I don't play many 2D platformer games, so maybe I'm missing some obvious reason. Where have you played this on? PC or Ipod Touch/Iphone? I heard the Iphone version have bad control, but I think they have fixed this by now link.
That was my thinking, too, and I liked the game. Please share your oppinion with us after playing.

I don't know if the game is terribly bad but I really didn't enjoy it. I played more than 2 hours, it's funny, cute and everything but I got bored. I rescued the little guys, fought a bunch of bosses etc... the environment was always the same and I thought it was hard to reach some platforms due to some bad collisions with the rocks.
I had more fun playing Cave story for instance. :)

Well, thanks for the honesty. I'll give Cave story a try. Could you explain about what is the game?

Cave Story is also a 2D platformer, but it's more action-oriented with countless of bosses to kill. It kind of reminds games like Metroid or Turrican. and on top of that, the storyline is amusing.

Everyone should be aware of this: