Picross is one of the best flash puzzles that's come down Little Fluffy Lane in a long time. A little reminiscent of Minesweeper, the rules are simple.

(1) Squares are either filled or empty.
(2) The numbers before each row or on top of that column indicate exactly the pattern of filled squares in that row or column.

For instance, if the number says "4", that means there are four filled squares in a row in that column, and the rest are empties.

If the number says "4 5", that means there are four filled squares in a row in that column, some number of empty squares, and then five filled squares in a row (and then empties, in any squares are left).

"2 1 2 1" means the pattern in that row is two filled squares, some number of empties, 1 filled square, some number of empties, 2 filled squares in a row, some number of empties, and then one filled square (and then empties, if any squares are left).

And so on.

It's a logic puzzle; your goal is to figure out the position of filleds and empties in the whole grid. At the end of each level, you're rewarded with the semi-abstract picture you just uncovered.

Fun.

There's a javascript Picross applet (with only three puzzles on smaller playing fields) here. This is where I found the rules originally, so I wanted to give them a little linking love, too.