Knytt
Knytt Stories
Within A Deep Forest
Art of Theft
Braid
Cave Story
Tripline
what are these about?
Knytt, Knytt Stories, and Within a Deep Forest are roughly similar. They were all made by Nifflas, who has a special fondness in his heart for artistically combining sound and scenery for a very interesting experience. Although the gameplay is almost always limited to getting from point A to point B, its how you do it that proves entertaining, and Within a Deep Forest explores this a different way by making you a bouncing ball. You can see a let's play of Knytt and Knytt Stories
here. I believe Knytt Stories also allows you to explore user-made content if you want to.
Art of Theft is a game by Ben "Yahtzee" Croshaw. You're a thief. You steal stuff. The gameplay is very entertaining, albeit just as difficult.
Braid is... well, it's Braid. It has its own
wikipedia page.
Yahtzee reviewed it. Just check those, they will do better justice to the game than I can.
Cave Story can be best summed up as something that looks and controls like a Mario game with guns, but has a story and platforming aspect more in line with the Castlevania series than Mario. More info regarding its origin and how to get it can be found
here, at it's Let's Play page in the Something Awful Let's Play archive.
Finally, Tripline is a puzzle game. It has its own particular gimmick and the degree of planning you have to take before you do anything makes it feel like sudoku. The whole game is a series of premade levels. At which point the game ends, I don't know.