I wrote Brick Breaker as a full-featured, polished PICO-8 sample program. It was an opportunity for me to learn the PICO-8 Lua variant and now stands as a good example program for other programmers new to PICO-8.
It demonstrates (commented) use of:

loops
create & destroy objects
local vars
text
multiple levels
sprite animation
powerups
particles
map usage
title screen & game over
sound effects
music
sprite packing
basic physics
assertions

as well as some techniques for reducing token count, a limited resource on PICO-8.
I did most of this work in parallel with the 2017 Global Game Jam. The PICO-8 version of Brick Breaker is based on my JavaScript Brick Breaker sample program, which you can play here.