Since the last post, I re-implemented the exploding brick type and the SFX that I lost, and created a level editor that imports .tmx level layouts from Tiled. I have a layer for brick colours, a layer for brick types (1hp, 2hp, multiball, indestructible bricks, etc), and a layer for powerups. There's also an 'extend paddle' powerup.
I'd say this is somewhere in between Breakout and Arkanoid/Brickout in terms of features. I think I've learned everything that I set out to learn from it, so I'm going to shelve it for now.