Filler is a game that will seem instantly familiar to you. If you've ever played JezzBall, or Barrack, or any of the clones thereof, you'll recognize the principle of Filler -- there's a number of balls bouncing around the screen, and your object is to claim as much of the screen as possible by placing objects on it. However, merely calling Filler a clone of those games would be quite inaccurate; there are major differences in Filler which make the gameplay substantially different.
First of all, in contrast to the aforementioned games (in which you claim territory by shooting lines across the playfield), in Filler you click and hold to draw a circle. The longer you hold the button, the bigger the circle becomes, but if a ball should hit you while your circle is still being drawn, then you lose a life and the circle vanishes. You can move the circle around while it's being placed, and once it has been placed, it can still be moved by gravity or by the action of the enemy balls hitting it.
The fact that balls can move after being placed creates a much more dynamic playfield than in traditional games of this type. For instance, you can drop balls from the top onto other balls to move them into more advantageous positions. You can also create balls in safe locations of the playfield and let them fall or slide into less safe areas. Conversely, it's much harder to trap enemy balls in a specific location because they can dislodge the balls that you've placed to block them (unless they're totally surrounded). This opens up new directions of strategy.
Unfortunately, the other major change has less beneficial effects. In JezzBall, for instance, once you've started firing a line, you can't stop until it hits the wall. However, the fact that you can release the mouse button and stop drawing the circle at any time means that you can get out of danger much more easily. (You do have a limited total number of balls that you can place, but in my experience this never became an issue.) This makes the game significantly easier than its counterparts; in fact, on my first play through, I ended up getting all of the badges for the game.
The graphics are exceedingly plain, and there's not much in the way of sound effects. The background music is kind of ethereal and relaxing, but it's not anything you'll be wanting to find a copy of for yourself or anything. Overall, the presentation is nothing special. So in summary, this is an interesting concept, but it really needs more attention to the game balance in order to be a truly fascinating game.