Wow - your comment tripped a memory in me. I learned on a TI and made heavy use of CALL CHAR to redefine the bit pattern for characters to draw on screen. I had a hard time switching to Commodore Basic because it wasn't clear to me how to accomplish similar things there.
Atari with their player-missile graphics made immediate sense to me though.
The code was out in the open and decipherable. Great way to learn in that particular environment.