http://www.helles-koepfchen.de/artikel/833.htmlhere's an exmaple of how I know the game (though I've never played it with these round bricks. but the shape of the bricks shouldn't matter).
Not also the bar at the bottom: it's slanted and depending on where the ball hits it behaves differently. It creates a fun challange, because that way you can decide where the ball should go.
In the breakout game I know, it's the goal to get rid of all the boxes (some are breakable, others aren't, so it gets harder) and then, when all breakable boxes are gone, it starts the next level (where it sets up the boxes in a new way, maybe with more different types of boxes).
You can also add upgrades that fall down when you break a certain type of block (either always let the same item fall down when you break a red block or always choose a random item that falls down). Examples: More balls, larger player bar, faster ball, slower ball, lasers that the player can shoot with (from the bar, upwards, in order to hit items)
Later on you can also add one or two moving blocks that slide from left to right and back -> more challange for the player.