I'm back with some very interesting information...
First off, I mentioned that bricks are hit only when shot with a same-coloured beam. That's true but in one case: white bricks react to beams of any color (it's always been like this, but I forgot to mention it).
Then, I said that each type of brick reacts in its own way - with the aid of the screenshot below, I'll describe in detail the types currently available (I plan to add more):
(Types indicated by the numbers on the left of bricks.)
Type #1: "normal" bricks. When hit, they disappear.
Type #2: "hard" bricks. They must be hit multiple times before they disappear. The number of hits required is visually indicated by the fill level (they visually "discharge" as they are hit). There are four variants, requiring 2 to 5 hits (the picture shows only the variants that require 3 and 5 hits).
Type #3: "ballbox" bricks. When hit, they generate a rebounding ball that hits/kills other bricks.
(Inspired by Arkanoid.)
Type #4: "region" bricks. When one of these bricks is hit, it disappears and the place where it was is marked with a flashing icon; then, when any other brick is hit, the places where hits happened are considered opposite corners of a rectangular region, and, for half a second, any brick that is/falls in such region is hit/killed.
(Inspired by Qix.)
Type #5: "brake" bricks. When hit, they stop the spawning of other bricks and halve the speed of the current bricks for 5 seconds.
(Inspired by Oils Well.)
Type #6: "split" bricks. When hit, they split into two other bricks of the same color and of random kind.
(Inspired by Pang.)
Type #7: "chameleon" brick. When hit, they morph into another brick of a random type and color.
Type #8 (bricks not marked): "bladebox" bricks. When hit, they fire a row of blades that hit/kill other bricks in every of the directions indicated visually (f.ex., the topmost brick fires blades in all directions, whereas the bottommost brick fires blades only downwards).
(I had this idea without looking for inspiration, but the effect is similar - albeit not identical - to that of flames in Bomberman.)
For a better understanding of how the "region" bricks work, here are a few screenshots showing the process.
Step #1: a purple "region" brick was falling and I got ready to hit it.
Step #2: I shot at the brick, which disappeared and left a white mark indicating where it was when it got hit.
Step #3: I moved 3 places to the right and shot at another brick. The area "between" the two hits got marked.
Step #4: all the bricks included in the area disappeared (incidentally, the second brick I hit was of "bladebox" kind, so also two rows of blades spawned - they are visible also in the previous screenshot).
One last note about hits: previously I had said that bricks hit by anything other than beams shot by the player would be just destroyed and then I had added a footnote saying that, instead, I would have modified that behaviour so that bricks would have reacted normally. Well, things have changed again: both cases are possible, depending on whether the "chain mode" is active or not - when the chain mode is off, bricks are just destroyed; when it's on, bricks are hit normally. The practical result is that when the chain mode is on (lots of) chain reactions can happen.
As usual, more will be said later...
