Picross (a.k.a. Nonogram) are Japanese logic puzzles where a picture is revealed by filling out spots in a grid using numbers on the columns/rows. For example, if there is a 1 1 1 on the side, then there will be three individual spots filled out with at least one empty spot between each one. Usually Picross puzzles come in either 5x5, 10x10, or 15x15 configurations. It also helps to have grown up with pixel art to try to determine what the picture actually is (especially on the 5x5 ones).
I'm pretty addicted to these puzzles types (if Sudoku made pictures when complete, I'd probably be equally addicted to that) and have played through/bought pretty much every instance of it I've seen. Online versions like Armor Picross and Armor Picross 2, DS versions like Picross DS and Picross 3D, 3DS versions like Picross e, Picross e2, and soon Picross e3 (just came out yesterday), and Kindle Fire versions like the Flippix Art series, CrossMe Color, and Picranium Picross (of course I always wait for those to show up as Amazon's free app of the day).
If you play one Picross game, generally you play them all (unless it's a color version since that changes how the puzzles/number system actually work). There are minor differences in how the input works. For example, are mistakes pointed out immediately (usually with a time penalty or a limited number of allowed mistakes) or can you build the remainder of the puzzle based off of a mistake? Can you zoom into the 15x15 grid or do you have to be a little too accurate? When you're done, do they turn the pixel pictures into a real picture or color it so it's easier to see what they are saying it is? If you have never played a Picross game, I'd start with one of the free online ones to see what you think about it. The Armor Picross series is very well done, so I'd start there. Enjoy and don't spend too much of your day on it!