Nice job. I've seen a couple of these interactive DOM games (breakout is especially popular) but 99% of them have been Firefox/Chrome extensions so it's nice to see one that is a simple bookmark.

If you wanted to get really crazy, you could take it a step further and change things based on each word’s part of speech. Such as you could alter the behavior of the game so that proper nouns become “tougher” blocks.

The default mode already does something along those lines — certain elements take two hits to break. But for the hidden B-side mode I went in the completely opposite direction: the ball phases through everything by default. See if you can find it ;)