These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Breather Level: Areas 3, 6, and 9, short space station stages with loads of destructible tiles, jazzy music, and fairly easy bosses.
Game Breaker: The Laser Power-up. Homes in on enemies, can pierce through obstacles, clear out groups of enemies, relatively strong, the works. Oh, and it's also available at the first stage.
There are situations when you might prefer one of the other weapons, but the Laser is pretty much always a good choice regardless of the situation. (Area 8 is the one exception, because you need something that won't hit the walls.)
Good Bad Bugs: Charge charges up faster if you toggle it into "no bullets" mode. If you start charging in this mode, but then toggle bullets back on, the charge will still increase at the same rate.